/*
 * oauth2-oidc-sdk
 *
 * Copyright 2012-2016, Connect2id Ltd and contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the
 * License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed
 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
 * CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */

package com.nimbusds.oauth2.sdk.as;


import com.nimbusds.jose.Algorithm;
import com.nimbusds.jose.EncryptionMethod;
import com.nimbusds.jose.JWEAlgorithm;
import com.nimbusds.jose.JWSAlgorithm;
import com.nimbusds.jose.jwk.JWKSet;
import com.nimbusds.langtag.LangTag;
import com.nimbusds.langtag.LangTagException;
import com.nimbusds.oauth2.sdk.*;
import com.nimbusds.oauth2.sdk.auth.ClientAuthenticationMethod;
import com.nimbusds.oauth2.sdk.ciba.BackChannelTokenDeliveryMode;
import com.nimbusds.oauth2.sdk.client.ClientType;
import com.nimbusds.oauth2.sdk.http.HTTPRequest;
import com.nimbusds.oauth2.sdk.http.HTTPRequestConfigurator;
import com.nimbusds.oauth2.sdk.http.HTTPResponse;
import com.nimbusds.oauth2.sdk.id.Identifier;
import com.nimbusds.oauth2.sdk.id.Issuer;
import com.nimbusds.oauth2.sdk.pkce.CodeChallengeMethod;
import com.nimbusds.oauth2.sdk.rar.AuthorizationType;
import com.nimbusds.oauth2.sdk.util.*;
import com.nimbusds.openid.connect.sdk.Prompt;
import com.nimbusds.openid.connect.sdk.federation.registration.ClientRegistrationType;
import com.nimbusds.openid.connect.sdk.op.EndpointName;
import net.minidev.json.JSONObject;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.*;


/**
 * OAuth 2.0 Authorisation Server (AS) metadata.
 *
 * <p>Related specifications:
 *
 * <ul>
 *     <li>OAuth 2.0 Authorization Server Metadata (RFC 8414)
 *     <li>OAuth 2.0 Mutual TLS Client Authentication and Certificate Bound
 *         Access Tokens (RFC 8705)
 *     <li>OAuth 2.0 Demonstrating Proof-of-Possession at the Application Layer
 *         (DPoP) (RFC 9449)
 *     <li>Financial-grade API: JWT Secured Authorization Response Mode for
 *         OAuth 2.0 (JARM)
 *     <li>OAuth 2.0 Authorization Server Issuer Identification (RFC 9207)
 *     <li>Financial-grade API - Part 2: Read and Write API Security Profile
 *     <li>OAuth 2.0 Pushed Authorization Requests (RFC 9126)
 *     <li>OAuth 2.0 Rich Authorization Requests (RFC 9396)
 *     <li>OAuth 2.0 Device Authorization Grant (RFC 8628)
 *     <li>OpenID Connect Client Initiated Backchannel Authentication Flow -
 *         Core 1.0
 *     <li>OAuth 2.0 Incremental Authorization
 *         (draft-ietf-oauth-incremental-authz)
 *     <li>Initiating User Registration via OpenID Connect 1.0
 *     <li>OpenID Connect Federation 1.0
 * </ul>
 */
public class AuthorizationServerMetadata extends AuthorizationServerEndpointMetadata implements ReadOnlyAuthorizationServerMetadata {

        /**
         * The registered parameter names.
         */
        private static final Set<String> REGISTERED_PARAMETER_NAMES;

        static {
                Set<String> p = new HashSet<>(AuthorizationServerEndpointMetadata.getRegisteredParameterNames());
                p.add("issuer");
                p.add("jwks_uri");
                p.add("scopes_supported");
                p.add("response_types_supported");
                p.add("response_modes_supported");
                p.add("grant_types_supported");
                p.add("code_challenge_methods_supported");
                p.add("token_endpoint_auth_methods_supported");
                p.add("token_endpoint_auth_signing_alg_values_supported");
                p.add("request_parameter_supported");
                p.add("request_uri_parameter_supported");
                p.add("require_request_uri_registration");
                p.add("request_object_signing_alg_values_supported");
                p.add("request_object_encryption_alg_values_supported");
                p.add("request_object_encryption_enc_values_supported");
                p.add("ui_locales_supported");
                p.add("service_documentation");
                p.add("op_policy_uri");
                p.add("op_tos_uri");
                p.add("introspection_endpoint_auth_methods_supported");
                p.add("introspection_endpoint_auth_signing_alg_values_supported");
                p.add("revocation_endpoint_auth_methods_supported");
                p.add("revocation_endpoint_auth_signing_alg_values_supported");
                p.add("mtls_endpoint_aliases");
                p.add("tls_client_certificate_bound_access_tokens");
                p.add("dpop_signing_alg_values_supported");
                p.add("authorization_signing_alg_values_supported");
                p.add("authorization_encryption_alg_values_supported");
                p.add("authorization_encryption_enc_values_supported");
                p.add("require_pushed_authorization_requests");
                p.add("authorization_details_types_supported");
                p.add("incremental_authz_types_supported");
                p.add("authorization_response_iss_parameter_supported");
                p.add("backchannel_token_delivery_modes_supported");
                p.add("backchannel_authentication_request_signing_alg_values_supported");
                p.add("backchannel_user_code_parameter_supported");
                p.add("prompt_values_supported");
                p.add("organization_name");
                p.add("jwks");
                p.add("signed_jwks_uri");
                p.add("client_registration_types_supported");
                p.add("request_authentication_methods_supported");
                p.add("request_authentication_signing_alg_values_supported");
                p.add("federation_registration_endpoint");
                REGISTERED_PARAMETER_NAMES = Collections.unmodifiableSet(p);
        }
        
        
        /**
         * Gets the registered OpenID Connect provider metadata parameter
         * names.
         *
         * @return The registered OpenID Connect provider metadata parameter
         *         names, as an unmodifiable set.
         */
        public static Set<String> getRegisteredParameterNames() {
                
                return REGISTERED_PARAMETER_NAMES;
        }
        
        
        /**
         * The issuer.
         */
        private final Issuer issuer;
        
        
        /**
         * The JWK set URI.
         */
        private URI jwkSetURI;
        
        
        /**
         * The supported scope values.
         */
        private Scope scope;
        
        
        /**
         * The supported response types.
         */
        private List<ResponseType> rts;
        
        
        /**
         * The supported response modes.
         */
        private List<ResponseMode> rms;
        
        
        /**
         * The supported grant types.
         */
        private List<GrantType> gts;
        
        
        /**
         * The supported code challenge methods for PKCE.
         */
        private List<CodeChallengeMethod> codeChallengeMethods;
        
        
        /**
         * The supported token endpoint authentication methods.
         */
        private List<ClientAuthenticationMethod> tokenEndpointAuthMethods;
        
        
        /**
         * The supported JWS algorithms for the {@code private_key_jwt} and
         * {@code client_secret_jwt} token endpoint authentication methods.
         */
        private List<JWSAlgorithm> tokenEndpointJWSAlgs;
        
        
        /**
         * The supported introspection endpoint authentication methods.
         */
        private List<ClientAuthenticationMethod> introspectionEndpointAuthMethods;
        
        
        /**
         * The supported JWS algorithms for the {@code private_key_jwt} and
         * {@code client_secret_jwt} introspection endpoint authentication
         * methods.
         */
        private List<JWSAlgorithm> introspectionEndpointJWSAlgs;
        
        
        /**
         * The supported revocation endpoint authentication methods.
         */
        private List<ClientAuthenticationMethod> revocationEndpointAuthMethods;
        
        
        /**
         * The supported JWS algorithms for the {@code private_key_jwt} and
         * {@code client_secret_jwt} revocation endpoint authentication
         * methods.
         */
        private List<JWSAlgorithm> revocationEndpointJWSAlgs;
        
        
        /**
         * The supported JWS algorithms for request objects.
         */
        private List<JWSAlgorithm> requestObjectJWSAlgs;
        
        
        /**
         * The supported JWE algorithms for request objects.
         */
        private List<JWEAlgorithm> requestObjectJWEAlgs;
        
        
        /**
         * The supported encryption methods for request objects.
         */
        private List<EncryptionMethod> requestObjectJWEEncs;
        
        
        /**
         * If {@code true} the {@code request} parameter is supported, else
         * not.
         */
        private boolean requestParamSupported = false;
        
        
        /**
         * If {@code true} the {@code request_uri} parameter is supported, else
         * not.
         */
        private boolean requestURIParamSupported = false;
        
        
        /**
         * If {@code true} the {@code request_uri} parameters must be
         * pre-registered with the provider, else not.
         */
        private boolean requireRequestURIReg = false;
        
        
        /**
         * If {@code true} the {@code iss} authorisation response is supported,
         * else not.
         */
        private boolean authzResponseIssParameterSupported = false;
        
        
        /**
         * The supported UI locales.
         */
        private List<LangTag> uiLocales;
        
        
        /**
         * The service documentation URI.
         */
        private URI serviceDocsURI;
        
        
        /**
         * The provider's policy regarding relying party use of data.
         */
        private URI policyURI;
        
        
        /**
         * The provider's terms of service.
         */
        private URI tosURI;
        
        
        /**
         * Aliases for endpoints with mutial TLS authentication.
         */
        private AuthorizationServerEndpointMetadata mtlsEndpointAliases;
        
        
        /**
         * If {@code true} the
         * {@code tls_client_certificate_bound_access_tokens} if set, else
         * not.
         */
        private boolean tlsClientCertificateBoundAccessTokens = false;
        
        
        /**
         * The supported JWS algorithms for DPoP.
         */
        private List<JWSAlgorithm> dPoPJWSAlgs;
        
        
        /**
         * The supported JWS algorithms for JWT-encoded authorisation
         * responses.
         */
        private List<JWSAlgorithm> authzJWSAlgs;
        
        
        /**
         * The supported JWE algorithms for JWT-encoded authorisation
         * responses.
         */
        private List<JWEAlgorithm> authzJWEAlgs;
        
        
        /**
         * The supported encryption methods for JWT-encoded authorisation
         * responses.
         */
        private List<EncryptionMethod> authzJWEEncs;
        
        
        /**
         * If {@code true} PAR is required, else not.
         */
        private boolean requirePAR = false;


        /**
         * The supported authorisation details types.
         */
        private List<AuthorizationType> authzTypes;
        
        
        /**
         * The supported OAuth 2.0 client types for incremental authorisation.
         */
        private List<ClientType> incrementalAuthzTypes;

        
        /**
         * The supported CIBA token delivery modes.
         */
        private List<BackChannelTokenDeliveryMode> backChannelTokenDeliveryModes;
        
        
        /**
         * The supported JWS algorithms for CIBA requests. If omitted signed
         * authentication requests are not supported.
         */
        private List<JWSAlgorithm> backChannelAuthRequestJWSAlgs;

        
        /**
         * If {@code true} the CIBA {@code user_code} parameter is supported,
         * else not.
         */
        private boolean backChannelUserCodeSupported = false;
        
        
        /**
         * The supported prompt types.
         */
        private List<Prompt.Type> promptTypes;
        
        
        /**
         * The organisation name (OpenID Connect Federation 1.0).
         */
        private String organizationName;
        
        
        /**
         * The OP JWK set (OpenID Connect Federation 1.0).
         */
        private JWKSet jwkSet;
        
        
        /**
         * The signed OP JWK set (OpenID Connect Federation 1.0).
         */
        private URI signedJWKSetURI;
        
        
        /**
         * The supported OpenID Connect Federation 1.0 client registration
         * types.
         */
        private List<ClientRegistrationType> clientRegistrationTypes;
        
        
        /**
         * The supported request authentication methods for automatic OpenID
         * Connect Federation 1.0 client registration.
         */
        private Map<EndpointName,List<ClientAuthenticationMethod>> clientRegistrationAuthMethods;
        
        
        /**
         * The supported JWS algorithms for authenticating automatic OpenID
         * Connect Federation 1.0 client registration requests.
         */
        private List<JWSAlgorithm> clientRegistrationAuthJWSAlgs;
        
        
        /**
         * The OpenID Connect Federation 1.0 registration endpoint.
         */
        private URI federationRegistrationEndpoint;
        
        
        /**
         * Custom (not-registered) parameters.
         */
        private final JSONObject customParameters = new JSONObject();
        
        
        /**
         * Creates a new OAuth 2.0 Authorisation Server (AS) metadata instance.
         *
         * @param issuer The issuer identifier. Must be a URI using the https
         *               scheme with no query or fragment component. Must not
         *               be {@code null}.
         */
        public AuthorizationServerMetadata(final Issuer issuer) {
                
                URI uri;
                try {
                        uri = new URI(issuer.getValue());
                } catch (URISyntaxException e) {
                        throw new IllegalArgumentException("The issuer identifier must be a URI: " + e.getMessage(), e);
                }
                
                if (uri.getRawQuery() != null)
                        throw new IllegalArgumentException("The issuer URI must be without a query component");
                
                if (uri.getRawFragment() != null)
                        throw new IllegalArgumentException("The issuer URI must be without a fragment component");
                
                this.issuer = issuer;
        }
        
        
        @Override
        public Issuer getIssuer() {
                return issuer;
        }
        
        
        @Override
        public URI getJWKSetURI() {
                return jwkSetURI;
        }
        
        
        /**
         * Sets the JSON Web Key (JWT) set URI. Corresponds to the
         * {@code jwks_uri} metadata field.
         *
         * @param jwkSetURI The JWK set URI, {@code null} if not specified.
         */
        public void setJWKSetURI(final URI jwkSetURI) {
                this.jwkSetURI = jwkSetURI;
        }
        
        
        @Override
        public Scope getScopes() {
                return scope;
        }
        
        
        /**
         * Sets the supported scope values. Corresponds to the
         * {@code scopes_supported} metadata field.
         *
         * @param scope The supported scope values, {@code null} if not
         *              specified.
         */
        public void setScopes(final Scope scope) {
                this.scope = scope;
        }
        
        
        @Override
        public List<ResponseType> getResponseTypes() {
                return rts;
        }
        
        
        /**
         * Sets the supported response type values. Corresponds to the
         * {@code response_types_supported} metadata field.
         *
         * @param rts The supported response type values, {@code null} if not
         *            specified.
         */
        public void setResponseTypes(final List<ResponseType> rts) {
                this.rts = rts;
        }
        
        
        @Override
        public List<ResponseMode> getResponseModes() {
                return rms;
        }
        
        
        /**
         * Sets the supported response mode values. Corresponds to the
         * {@code response_modes_supported}.
         *
         * @param rms The supported response mode values, {@code null} if not
         *            specified.
         */
        public void setResponseModes(final List<ResponseMode> rms) {
                this.rms = rms;
        }
        
        
        @Override
        public List<GrantType> getGrantTypes() {
                return gts;
        }
        
        
        /**
         * Sets the supported OAuth 2.0 grant types. Corresponds to the
         * {@code grant_types_supported} metadata field.
         *
         * @param gts The supported grant types, {@code null} if not specified.
         */
        public void setGrantTypes(final List<GrantType> gts) {
                this.gts = gts;
        }
        
        
        @Override
        public List<CodeChallengeMethod> getCodeChallengeMethods() {
                return codeChallengeMethods;
        }
        
        
        /**
         * Gets the supported authorisation code challenge methods for PKCE.
         * Corresponds to the {@code code_challenge_methods_supported} metadata
         * field.
         *
         * @param codeChallengeMethods The supported code challenge methods,
         *                             {@code null} if not specified.
         */
        public void setCodeChallengeMethods(final List<CodeChallengeMethod> codeChallengeMethods) {
                this.codeChallengeMethods = codeChallengeMethods;
        }
        
        
        @Override
        public List<ClientAuthenticationMethod> getTokenEndpointAuthMethods() {
                return tokenEndpointAuthMethods;
        }
        
        
        /**
         * Sets the supported token endpoint authentication methods.
         * Corresponds to the {@code token_endpoint_auth_methods_supported}
         * metadata field.
         *
         * @param authMethods The supported token endpoint authentication
         *                    methods, {@code null} if not specified.
         */
        public void setTokenEndpointAuthMethods(final List<ClientAuthenticationMethod> authMethods) {
                this.tokenEndpointAuthMethods = authMethods;
        }
        
        
        @Override
        public List<JWSAlgorithm> getTokenEndpointJWSAlgs() {
                return tokenEndpointJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for the {@code private_key_jwt}
         * and {@code client_secret_jwt} token endpoint authentication methods.
         * Corresponds to the
         * {@code token_endpoint_auth_signing_alg_values_supported} metadata
         * field.
         *
         * @param jwsAlgs The supported JWS algorithms, {@code null} if not
         *                specified. Must not contain the {@code none}
         *                algorithm.
         */
        public void setTokenEndpointJWSAlgs(final List<JWSAlgorithm> jwsAlgs) {
                if (jwsAlgs != null && jwsAlgs.contains(Algorithm.NONE))
                        throw new IllegalArgumentException("The \"none\" algorithm is not accepted");
                
                this.tokenEndpointJWSAlgs = jwsAlgs;
        }
        
        
        @Override
        public List<ClientAuthenticationMethod> getIntrospectionEndpointAuthMethods() {
                return introspectionEndpointAuthMethods;
        }
        
        
        /**
         * Sets the supported introspection endpoint authentication methods.
         * Corresponds to the
         * {@code introspection_endpoint_auth_methods_supported} metadata
         * field.
         *
         * @param authMethods The supported introspection endpoint
         *                    authentication methods, {@code null} if not
         *                    specified.
         */
        public void setIntrospectionEndpointAuthMethods(final List<ClientAuthenticationMethod> authMethods) {
                this.introspectionEndpointAuthMethods = authMethods;
        }
        
        
        @Override
        public List<JWSAlgorithm> getIntrospectionEndpointJWSAlgs() {
                return introspectionEndpointJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for the {@code private_key_jwt}
         * and {@code client_secret_jwt} introspection endpoint authentication
         * methods. Corresponds to the
         * {@code introspection_endpoint_auth_signing_alg_values_supported}
         * metadata field.
         *
         * @param jwsAlgs The supported JWS algorithms, {@code null} if not
         *                specified. Must not contain the {@code none}
         *                algorithm.
         */
        public void setIntrospectionEndpointJWSAlgs(final List<JWSAlgorithm> jwsAlgs) {
                
                if (jwsAlgs != null && jwsAlgs.contains(Algorithm.NONE))
                        throw new IllegalArgumentException("The \"none\" algorithm is not accepted");
                
                introspectionEndpointJWSAlgs = jwsAlgs;
        }
        
        
        @Override
        public List<ClientAuthenticationMethod> getRevocationEndpointAuthMethods() {
                return revocationEndpointAuthMethods;
        }
        
        
        /**
         * Sets the supported revocation endpoint authentication methods.
         * Corresponds to the
         * {@code revocation_endpoint_auth_methods_supported} metadata field.
         *
         * @param authMethods The supported revocation endpoint authentication
         *                    methods, {@code null} if not specified.
         */
        public void setRevocationEndpointAuthMethods(final List<ClientAuthenticationMethod> authMethods) {
                revocationEndpointAuthMethods = authMethods;
        }
        
        
        @Override
        public List<JWSAlgorithm> getRevocationEndpointJWSAlgs() {
                return revocationEndpointJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for the {@code private_key_jwt}
         * and {@code client_secret_jwt} revocation endpoint authentication
         * methods. Corresponds to the
         * {@code revocation_endpoint_auth_signing_alg_values_supported}
         * metadata field.
         *
         * @param jwsAlgs The supported JWS algorithms, {@code null} if not
         *                specified. Must not contain the {@code none}
         *                algorithm.
         */
        public void setRevocationEndpointJWSAlgs(final List<JWSAlgorithm> jwsAlgs) {
                
                if (jwsAlgs != null && jwsAlgs.contains(Algorithm.NONE))
                        throw new IllegalArgumentException("The \"none\" algorithm is not accepted");
                
                revocationEndpointJWSAlgs = jwsAlgs;
        }
        
        
        @Override
        public List<JWSAlgorithm> getRequestObjectJWSAlgs() {
                return requestObjectJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for request objects. Corresponds
         * to the {@code request_object_signing_alg_values_supported} metadata
         * field.
         *
         * @param requestObjectJWSAlgs The supported JWS algorithms,
         *                             {@code null} if not specified.
         */
        public void setRequestObjectJWSAlgs(final List<JWSAlgorithm> requestObjectJWSAlgs) {
                this.requestObjectJWSAlgs = requestObjectJWSAlgs;
        }
        
        
        @Override
        public List<JWEAlgorithm> getRequestObjectJWEAlgs() {
                return requestObjectJWEAlgs;
        }
        
        
        /**
         * Sets the supported JWE algorithms for request objects. Corresponds
         * to the {@code request_object_encryption_alg_values_supported}
         * metadata field.
         *
         * @param requestObjectJWEAlgs The supported JWE algorithms,
         *                            {@code null} if not specified.
         */
        public void setRequestObjectJWEAlgs(final List<JWEAlgorithm> requestObjectJWEAlgs) {
                this.requestObjectJWEAlgs = requestObjectJWEAlgs;
        }
        
        
        @Override
        public List<EncryptionMethod> getRequestObjectJWEEncs() {
                return requestObjectJWEEncs;
        }
        
        
        /**
         * Sets the supported encryption methods for request objects.
         * Corresponds to the
         * {@code request_object_encryption_enc_values_supported} metadata
         * field.
         *
         * @param requestObjectJWEEncs The supported encryption methods,
         *                             {@code null} if not specified.
         */
        public void setRequestObjectJWEEncs(final List<EncryptionMethod> requestObjectJWEEncs) {
                this.requestObjectJWEEncs = requestObjectJWEEncs;
        }
        
        
        @Override
        public boolean supportsRequestParam() {
                return requestParamSupported;
        }
        
        
        /**
         * Sets the support for the {@code request} authorisation request
         * parameter. Corresponds to the {@code request_parameter_supported}
         * metadata field.
         *
         * @param requestParamSupported {@code true} if the {@code reqeust}
         *                              parameter is supported, else
         *                              {@code false}.
         */
        public void setSupportsRequestParam(final boolean requestParamSupported) {
                this.requestParamSupported = requestParamSupported;
        }
        
        
        @Override
        public boolean supportsRequestURIParam() {
                return requestURIParamSupported;
        }
        
        
        /**
         * Sets the support for the {@code request_uri} authorisation request
         * parameter. Corresponds to the
         * {@code request_uri_parameter_supported} metadata field.
         *
         * @param requestURIParamSupported {@code true} if the
         *                                 {@code request_uri} parameter is
         *                                 supported, else {@code false}.
         */
        public void setSupportsRequestURIParam(final boolean requestURIParamSupported) {
                this.requestURIParamSupported = requestURIParamSupported;
        }
        
        
        @Override
        public boolean requiresRequestURIRegistration() {
                return requireRequestURIReg;
        }
        
        
        /**
         * Sets the requirement for the {@code request_uri} parameter
         * pre-registration. Corresponds to the
         * {@code require_request_uri_registration} metadata field.
         *
         * @param requireRequestURIReg {@code true} if the {@code request_uri}
         *                             parameter values must be pre-registered,
         *                             else {@code false}.
         */
        public void setRequiresRequestURIRegistration(final boolean requireRequestURIReg) {
                this.requireRequestURIReg = requireRequestURIReg;
        }
        
        
        @Override
        public boolean supportsAuthorizationResponseIssuerParam() {
                return authzResponseIssParameterSupported;
        }
        
        
        /**
         * Sets the support for the {@code iss} authorisation response
         * parameter. Corresponds to the
         * {@code authorization_response_iss_parameter_supported} metadata
         * field.
         *
         * @param authzResponseIssParameterSupported {@code true} if the
         *                                           {@code iss} authorisation
         *                                           response parameter is
         *                                           provided, else
         *                                           {@code false}.
         */
        public void setSupportsAuthorizationResponseIssuerParam(final boolean authzResponseIssParameterSupported) {
                this.authzResponseIssParameterSupported = authzResponseIssParameterSupported;
        }
        
        
        @Override
        public List<LangTag> getUILocales() {
                return uiLocales;
        }
        
        
        /**
         * Sets the supported UI locales. Corresponds to the
         * {@code ui_locales_supported} metadata field.
         *
         * @param uiLocales The supported UI locales, {@code null} if not
         *                  specified.
         */
        public void setUILocales(final List<LangTag> uiLocales) {
                this.uiLocales = uiLocales;
        }
        
        
        @Override
        public URI getServiceDocsURI() {
                return serviceDocsURI;
        }
        
        
        /**
         * Sets the service documentation URI. Corresponds to the
         * {@code service_documentation} metadata field.
         *
         * @param serviceDocsURI The service documentation URI, {@code null} if
         *                       not specified. The URI scheme must be https or
         *                       http.
         */
        public void setServiceDocsURI(final URI serviceDocsURI) {
                URIUtils.ensureSchemeIsHTTPSorHTTP(serviceDocsURI);
                this.serviceDocsURI = serviceDocsURI;
        }
        
        
        @Override
        public URI getPolicyURI() {
                return policyURI;
        }
        
        
        /**
         * Sets the provider's policy regarding relying party use of data.
         * Corresponds to the {@code op_policy_uri} metadata field.
         *
         * @param policyURI The policy URI, {@code null} if not specified. The
         *                  URI scheme must be https or http.
         */
        public void setPolicyURI(final URI policyURI) {
                URIUtils.ensureSchemeIsHTTPSorHTTP(policyURI);
                this.policyURI = policyURI;
        }
        
        
        @Override
        public URI getTermsOfServiceURI() {
                return tosURI;
        }
        
        
        /**
         * Sets the provider's terms of service. Corresponds to the
         * {@code op_tos_uri} metadata field.
         *
         * @param tosURI The terms of service URI, {@code null} if not
         *               specified. The URI scheme must be https or http.
         */
        public void setTermsOfServiceURI(final URI tosURI) {
                URIUtils.ensureSchemeIsHTTPSorHTTP(tosURI);
                this.tosURI = tosURI;
        }
        
        
        @Override
        public ReadOnlyAuthorizationServerEndpointMetadata getReadOnlyMtlsEndpointAliases() {
                return getMtlsEndpointAliases();
        }
        
        
        /**
         * Gets the aliases for communication with mutual TLS. Corresponds to
         * the {@code mtls_endpoint_aliases} metadata field.
         *
         * @return The aliases for communication with mutual TLS, {@code null}
         *         when no aliases are defined.
         */
        public AuthorizationServerEndpointMetadata getMtlsEndpointAliases() {
                return mtlsEndpointAliases;
        }
        
        
        /**
         * Sets the aliases for communication with mutual TLS. Corresponds to the
         * {@code mtls_endpoint_aliases} metadata field.
         * 
         * @param mtlsEndpointAliases The aliases for communication with mutual
         *                            TLS, or {@code null} when no aliases are
         *                            defined.
         */
        public void setMtlsEndpointAliases(AuthorizationServerEndpointMetadata mtlsEndpointAliases) {
                this.mtlsEndpointAliases = mtlsEndpointAliases;
        }
        
        
        @Override
        public boolean supportsTLSClientCertificateBoundAccessTokens() {
                return tlsClientCertificateBoundAccessTokens;
        }
        
        
        /**
         * Sets the support for TLS client certificate bound access tokens.
         * Corresponds to the
         * {@code tls_client_certificate_bound_access_tokens} metadata field.
         *
         * @param tlsClientCertBoundTokens {@code true} if TLS client
         *                                 certificate bound access tokens are
         *                                 supported, else {@code false}.
         */
        public void setSupportsTLSClientCertificateBoundAccessTokens(final boolean tlsClientCertBoundTokens) {
                tlsClientCertificateBoundAccessTokens = tlsClientCertBoundTokens;
        }
        
        
        @Override
        @Deprecated
        public boolean supportsMutualTLSSenderConstrainedAccessTokens() {
                return supportsTLSClientCertificateBoundAccessTokens();
        }
        
        
        /**
         * Sets the support for TLS client certificate bound access tokens.
         * Corresponds to the
         * {@code tls_client_certificate_bound_access_tokens} metadata field.
         *
         * @param mutualTLSSenderConstrainedAccessTokens {@code true} if TLS
         *                                               client certificate
         *                                               bound access tokens
         *                                               are supported, else
         *                                               {@code false}.
         */
        @Deprecated
        public void setSupportsMutualTLSSenderConstrainedAccessTokens(final boolean mutualTLSSenderConstrainedAccessTokens) {
                setSupportsTLSClientCertificateBoundAccessTokens(mutualTLSSenderConstrainedAccessTokens);
        }
        
        
        @Override
        public List<JWSAlgorithm> getDPoPJWSAlgs() {
                return dPoPJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for Demonstrating
         * Proof-of-Possession at the Application Layer (DPoP). Corresponds to
         * the "dpop_signing_alg_values_supported" metadata field.
         *
         * @param dPoPJWSAlgs The supported JWS algorithms for DPoP,
         *                    {@code null} if none.
         */
        public void setDPoPJWSAlgs(final List<JWSAlgorithm> dPoPJWSAlgs) {
                this.dPoPJWSAlgs = dPoPJWSAlgs;
        }
        
        
        @Override
        public List<JWSAlgorithm> getAuthorizationJWSAlgs() {
                return authzJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for JWT-encoded authorisation
         * responses. Corresponds to the
         * {@code authorization_signing_alg_values_supported} metadata field.
         *
         * @param authzJWSAlgs The supported JWS algorithms, {@code null} if
         *                     not specified.
         */
        public void setAuthorizationJWSAlgs(final List<JWSAlgorithm> authzJWSAlgs) {
                this.authzJWSAlgs = authzJWSAlgs;
        }
        
        
        @Override
        public List<JWEAlgorithm> getAuthorizationJWEAlgs() {
                return authzJWEAlgs;
        }
        
        
        /**
         * Sets the supported JWE algorithms for JWT-encoded authorisation
         * responses. Corresponds to the
         * {@code authorization_encryption_alg_values_supported} metadata
         * field.
         *
         * @param authzJWEAlgs The supported JWE algorithms, {@code null} if
         *                     not specified.
         */
        public void setAuthorizationJWEAlgs(final List<JWEAlgorithm> authzJWEAlgs) {
                this.authzJWEAlgs = authzJWEAlgs;
        }
        
        
        @Override
        public List<EncryptionMethod> getAuthorizationJWEEncs() {
                return authzJWEEncs;
        }
        
        
        /**
         * Sets the supported encryption methods for JWT-encoded authorisation
         * responses. Corresponds to the
         * {@code authorization_encryption_enc_values_supported} metadata
         * field.
         *
         * @param authzJWEEncs The supported encryption methods, {@code null}
         *                     if not specified.
         */
        public void setAuthorizationJWEEncs(final List<EncryptionMethod> authzJWEEncs) {
                this.authzJWEEncs = authzJWEEncs;
        }
        
        
        @Override
        public boolean requiresPushedAuthorizationRequests() {
                return requirePAR;
        }
        
        
        /**
         * Sets the requirement for pushed authorisation requests (PAR).
         * Corresponds to the {@code pushed_authorization_request_endpoint}
         * metadata field.
         *
         * @param requirePAR {@code true} if PAR is required, else
         *                   {@code false}.
         */
        public void requiresPushedAuthorizationRequests(final boolean requirePAR) {
                this.requirePAR = requirePAR;
        }


        @Override
        public List<AuthorizationType> getAuthorizationDetailsTypes() {
                return authzTypes;
        }


        /**
         * Sets the supported authorisation details types for Rich
         * Authorisation Requests (RAR). Corresponds to the
         * {@code authorization_details_types_supported} metadata field.
         *
         * @param authzTypes The supported authorisation types, {@code null} if
         *                   not specified.
         */
        public void setAuthorizationDetailsTypes(final List<AuthorizationType> authzTypes) {
                this.authzTypes = authzTypes;
        }


        @Override
        public List<ClientType> getIncrementalAuthorizationTypes() {
                return incrementalAuthzTypes;
        }
        
        
        /**
         * Sets the supported OAuth 2.0 client types for incremental
         * authorisation. Corresponds to the
         * {@code incremental_authz_types_supported} metadata field.
         *
         * @param incrementalAuthzTypes The supported client types for
         *                              incremental authorisation, {@code null}
         *                              if not specified.
         */
        public void setIncrementalAuthorizationTypes(final List<ClientType> incrementalAuthzTypes) {
                this.incrementalAuthzTypes = incrementalAuthzTypes;
        }
        
        
        @Override
        public List<BackChannelTokenDeliveryMode> getBackChannelTokenDeliveryModes() {
                return backChannelTokenDeliveryModes;
        }
        
        
        /**
         * Sets the supported CIBA token delivery modes. Corresponds to the
         * {@code backchannel_token_delivery_modes_supported} metadata field.
         *
         * @param backChannelTokenDeliveryModes The CIBA token delivery modes,
         *                                      {@code null} if not specified.
         */
        public void setBackChannelTokenDeliveryModes(final List<BackChannelTokenDeliveryMode> backChannelTokenDeliveryModes) {
                this.backChannelTokenDeliveryModes = backChannelTokenDeliveryModes;
        }
        
        @Override
        public List<JWSAlgorithm> getBackChannelAuthenticationRequestJWSAlgs() {
                return backChannelAuthRequestJWSAlgs;
        }
        
        /**
         * Gets the supported JWS algorithms for CIBA requests. Corresponds to
         * the {@code backchannel_authentication_request_signing_alg_values_supported}
         * metadata field.
         *
         * @param backChannelAuthRequestJWSAlgs The supported JWS algorithms,
         *                                      {@code null} if not specified.
         */
        public void setBackChannelAuthenticationRequestJWSAlgs(final List<JWSAlgorithm> backChannelAuthRequestJWSAlgs) {
                this.backChannelAuthRequestJWSAlgs = backChannelAuthRequestJWSAlgs;
        }
        
        
        @Override
        public boolean supportsBackChannelUserCodeParam() {
                return backChannelUserCodeSupported;
        }
        
        
        /**
         * Sets the support for the {@code user_code} CIBA request parameter.
         * Corresponds to the {@code backchannel_user_code_parameter_supported}
         * metadata field.
         *
         * @param backChannelUserCodeSupported {@code true} if the
         *                                     {@code user_code} parameter is
         *                                     supported, else {@code false}.
         */
        public void setSupportsBackChannelUserCodeParam(final boolean backChannelUserCodeSupported) {
                this.backChannelUserCodeSupported = backChannelUserCodeSupported;
        }
        
        
        @Override
        public List<Prompt.Type> getPromptTypes() {
                return promptTypes;
        }
        
        
        /**
         * Sets the supported {@link Prompt.Type prompt types}. Corresponds to
         * the {@code prompt_values_supported} metadata field.
         *
         * @param promptTypes The supported prompt types, {@code null} if not
         *                    specified.
         */
        public void setPromptTypes(final List<Prompt.Type> promptTypes) {
                this.promptTypes = promptTypes;
        }
        
        
        @Override
        public String getOrganizationName() {
                return organizationName;
        }
        
        
        /**
         * Sets the organisation name (in federation). Corresponds to the
         * {@code organization_name} metadata field.
         *
         * @param organizationName The organisation name, {@code null} if not
         *                         specified.
         */
        public void setOrganizationName(final String organizationName) {
                this.organizationName = organizationName;
        }
        
        
        @Override
        public JWKSet getJWKSet() {
                return jwkSet;
        }
        
        
        /**
         * Sets the JWK set (OpenID Connect Federation 1.0). Corresponds to the
         * {@code jwks} metadata field.
         *
         * @param jwkSet The JWK set, {@code null} if not specified.
         */
        public void setJWKSet(final JWKSet jwkSet) {
                this.jwkSet = jwkSet;
        }
        
        
        @Override
        public URI getSignedJWKSetURI() {
                return signedJWKSetURI;
        }
        
        
        /**
         * Sets the signed JWK set URI (OpenID Connect Federation 1.0).
         * Corresponds to the {@code signed_jwks_uri} metadata field.
         *
         * @param signedJWKSetURI The signed JWK set URI, {@code null} if not
         *                        specified.
         */
        public void setSignedJWKSetURI(final URI signedJWKSetURI) {
                this.signedJWKSetURI = signedJWKSetURI;
        }
        
        
        @Override
        public List<ClientRegistrationType> getClientRegistrationTypes() {
                return clientRegistrationTypes;
        }
        
        
        /**
         * Sets the supported federation client registration types. Corresponds
         * to the {@code client_registration_types_supported} metadata field.
         *
         * @param clientRegistrationTypes The supported client registration
         *                                types, {@code null} if not specified.
         */
        public void setClientRegistrationTypes(final List<ClientRegistrationType> clientRegistrationTypes) {
                this.clientRegistrationTypes = clientRegistrationTypes;
        }
        
        
        @Override
        public Map<EndpointName, List<ClientAuthenticationMethod>> getClientRegistrationAuthnMethods() {
                return clientRegistrationAuthMethods;
        }
        
        
        /**
         * Sets the supported request authentication methods for automatic
         * OpenID Connect Federation 1.0 client registration. Corresponds to
         * the {@code request_authentication_methods_supported} field.
         *
         * @param methods The supported request authentication methods for
         *                automatic federation client registration,
         *                {@code null} if not specified.
         */
        public void setClientRegistrationAuthnMethods(final Map<EndpointName,List<ClientAuthenticationMethod>> methods) {
                clientRegistrationAuthMethods = methods;
        }
        
        
        @Override
        public List<JWSAlgorithm> getClientRegistrationAuthnJWSAlgs() {
                return clientRegistrationAuthJWSAlgs;
        }
        
        
        /**
         * Sets the supported JWS algorithms for authenticating automatic
         * OpenID Connect Federation 1.0 client registration requests.
         * Corresponds to the
         * {@code request_authentication_signing_alg_values_supported}.
         *
         * @param jwsAlgs The supported JWS algorithms, {@code null} if
         *                       not specified.
         */
        public void setClientRegistrationAuthnJWSAlgs(final List<JWSAlgorithm> jwsAlgs) {
                clientRegistrationAuthJWSAlgs = jwsAlgs;
        }
        
        
        @Override
        public URI getFederationRegistrationEndpointURI() {
                return federationRegistrationEndpoint;
        }
        
        
        /**
         * Sets the federation registration endpoint URI. Corresponds to the
         * {@code federation_registration_endpoint} metadata field.
         *
         * @param federationRegistrationEndpoint The federation registration
         *                                       endpoint URI, {@code null} if
         *                                       not specified.
         */
        public void setFederationRegistrationEndpointURI(final URI federationRegistrationEndpoint) {
                this.federationRegistrationEndpoint = federationRegistrationEndpoint;
        }
        
        
        @Override
        public Object getCustomParameter(final String name) {
                
                return customParameters.get(name);
        }
        
        
        @Override
        public URI getCustomURIParameter(final String name) {
                
                try {
                        return JSONObjectUtils.getURI(customParameters, name, null);
                } catch (ParseException e) {
                        return null;
                }
        }
        
        
        /**
         * Sets the specified custom (not registered) parameter.
         *
         * @param name  The parameter name. Must not be {@code null}.
         * @param value The parameter value, {@code null} if not specified.
         */
        public void setCustomParameter(final String name, final Object value) {
                
                if (REGISTERED_PARAMETER_NAMES.contains(name)) {
                        throw new IllegalArgumentException("The " + name + " parameter is registered");
                }
                
                customParameters.put(name, value);
        }
        
        
        @Override
        public JSONObject getCustomParameters() {
                
                return customParameters;
        }
        
        
        /**
         * Applies the OAuth 2.0 Authorisation Server metadata defaults where
         * no values have been specified.
         *
         * <ul>
         *     <li>The response modes default to {@code ["query", "fragment"]}.
         *     <li>The grant types default to {@code ["authorization_code",
         *         "implicit"]}.
         *     <li>The token endpoint authentication methods default to
         *         {@code ["client_secret_basic"]}.
         * </ul>
         */
        public void applyDefaults() {
                
                if (rms == null) {
                        rms = new ArrayList<>(2);
                        rms.add(ResponseMode.QUERY);
                        rms.add(ResponseMode.FRAGMENT);
                }
                
                if (gts == null) {
                        gts = new ArrayList<>(2);
                        gts.add(GrantType.AUTHORIZATION_CODE);
                        gts.add(GrantType.IMPLICIT);
                }
                
                if (tokenEndpointAuthMethods == null) {
                        tokenEndpointAuthMethods = new ArrayList<>();
                        tokenEndpointAuthMethods.add(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
                }
        }
        
        
        @Override
        public JSONObject toJSONObject() {
                JSONObject o = super.toJSONObject();
                
                // Mandatory fields
                o.put("issuer", issuer.getValue());
                
                
                // Optional fields
                if (jwkSetURI != null)
                        o.put("jwks_uri", jwkSetURI.toString());
                
                if (scope != null)
                        o.put("scopes_supported", scope.toStringList());
                
                List<String> stringList;
                
                if (rts != null) {
                        
                        stringList = new ArrayList<>(rts.size());
                        
                        for (ResponseType rt: rts)
                                stringList.add(rt.toString());
                        
                        o.put("response_types_supported", stringList);
                }
                
                if (rms != null) {
                        
                        stringList = new ArrayList<>(rms.size());
                        
                        for (ResponseMode rm: rms)
                                stringList.add(rm.getValue());
                        
                        o.put("response_modes_supported", stringList);
                }
                
                if (gts != null) {
                        
                        stringList = new ArrayList<>(gts.size());
                        
                        for (GrantType gt: gts)
                                stringList.add(gt.toString());
                        
                        o.put("grant_types_supported", stringList);
                }
                
                if (codeChallengeMethods != null) {
                        
                        stringList = new ArrayList<>(codeChallengeMethods.size());
                        
                        for (CodeChallengeMethod m: codeChallengeMethods)
                                stringList.add(m.getValue());
                        
                        o.put("code_challenge_methods_supported", stringList);
                }
                
                
                if (tokenEndpointAuthMethods != null) {
                        
                        stringList = new ArrayList<>(tokenEndpointAuthMethods.size());
                        
                        for (ClientAuthenticationMethod m: tokenEndpointAuthMethods)
                                stringList.add(m.getValue());
                        
                        o.put("token_endpoint_auth_methods_supported", stringList);
                }
                
                if (tokenEndpointJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(tokenEndpointJWSAlgs.size());
                        
                        for (JWSAlgorithm alg: tokenEndpointJWSAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("token_endpoint_auth_signing_alg_values_supported", stringList);
                }
                
                if (introspectionEndpointAuthMethods != null) {
                        
                        stringList = new ArrayList<>(introspectionEndpointAuthMethods.size());
                        
                        for (ClientAuthenticationMethod m: introspectionEndpointAuthMethods)
                                stringList.add(m.getValue());
                        
                        o.put("introspection_endpoint_auth_methods_supported", stringList);
                }
                
                if (introspectionEndpointJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(introspectionEndpointJWSAlgs.size());
                        
                        for (JWSAlgorithm alg: introspectionEndpointJWSAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("introspection_endpoint_auth_signing_alg_values_supported", stringList);
                }
                
                if (revocationEndpointAuthMethods != null) {
                        
                        stringList = new ArrayList<>(revocationEndpointAuthMethods.size());
                        
                        for (ClientAuthenticationMethod m: revocationEndpointAuthMethods)
                                stringList.add(m.getValue());
                        
                        o.put("revocation_endpoint_auth_methods_supported", stringList);
                }
                
                if (revocationEndpointJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(revocationEndpointJWSAlgs.size());
                        
                        for (JWSAlgorithm alg: revocationEndpointJWSAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("revocation_endpoint_auth_signing_alg_values_supported", stringList);
                }
                
                if (requestObjectJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(requestObjectJWSAlgs.size());
                        
                        for (JWSAlgorithm alg: requestObjectJWSAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("request_object_signing_alg_values_supported", stringList);
                }
                
                if (requestObjectJWEAlgs != null) {
                        
                        stringList = new ArrayList<>(requestObjectJWEAlgs.size());
                        
                        for (JWEAlgorithm alg: requestObjectJWEAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("request_object_encryption_alg_values_supported", stringList);
                }
                
                if (requestObjectJWEEncs != null) {
                        
                        stringList = new ArrayList<>(requestObjectJWEEncs.size());
                        
                        for (EncryptionMethod m: requestObjectJWEEncs)
                                stringList.add(m.getName());
                        
                        o.put("request_object_encryption_enc_values_supported", stringList);
                }
                
                if (uiLocales != null) {
                        
                        stringList = new ArrayList<>(uiLocales.size());
                        
                        for (LangTag l: uiLocales)
                                stringList.add(l.toString());
                        
                        o.put("ui_locales_supported", stringList);
                }
                
                if (serviceDocsURI != null)
                        o.put("service_documentation", serviceDocsURI.toString());
                
                if (policyURI != null)
                        o.put("op_policy_uri", policyURI.toString());
                
                if (tosURI != null)
                        o.put("op_tos_uri", tosURI.toString());
                
                if (requestParamSupported) {
                        o.put("request_parameter_supported", true);
                }
                
                if (requestURIParamSupported) {
                        o.put("request_uri_parameter_supported", true);
                }
                
                if (requireRequestURIReg) {
                        o.put("require_request_uri_registration", true);
                }
                
                if (authzResponseIssParameterSupported) {
                        o.put("authorization_response_iss_parameter_supported", true);
                }
                
                if (mtlsEndpointAliases != null)
                        o.put("mtls_endpoint_aliases", mtlsEndpointAliases.toJSONObject());
                
                if (tlsClientCertificateBoundAccessTokens) {
                        o.put("tls_client_certificate_bound_access_tokens", true);
                }
                
                // DPoP
                if (dPoPJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(dPoPJWSAlgs.size());
                        
                        for (JWSAlgorithm alg: dPoPJWSAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("dpop_signing_alg_values_supported", stringList);
                }
                
                // JARM
                if (authzJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(authzJWSAlgs.size());
                        
                        for (JWSAlgorithm alg: authzJWSAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("authorization_signing_alg_values_supported", stringList);
                }
                
                if (authzJWEAlgs != null) {
                        
                        stringList = new ArrayList<>(authzJWEAlgs.size());
                        
                        for (JWEAlgorithm alg: authzJWEAlgs)
                                stringList.add(alg.getName());
                        
                        o.put("authorization_encryption_alg_values_supported", stringList);
                }
                
                if (authzJWEEncs != null) {
                        
                        stringList = new ArrayList<>(authzJWEEncs.size());
                        
                        for (EncryptionMethod m: authzJWEEncs)
                                stringList.add(m.getName());
                        
                        o.put("authorization_encryption_enc_values_supported", stringList);
                }
                
                // PAR
                if (requirePAR) {
                        o.put("require_pushed_authorization_requests", true);
                }

                // RAR
                if (authzTypes != null) {
                        o.put("authorization_details_types_supported", Identifier.toStringList(authzTypes));
                }
                
                // Incremental authz
                if (CollectionUtils.isNotEmpty(incrementalAuthzTypes)) {
                        stringList = new ArrayList<>(incrementalAuthzTypes.size());
                        for (ClientType clientType: incrementalAuthzTypes) {
                                if (clientType != null) {
                                        stringList.add(clientType.name().toLowerCase());
                                }
                        }
                        o.put("incremental_authz_types_supported", stringList);
                }
                
                // CIBA
                if (backChannelTokenDeliveryModes != null) {
                        
                        stringList = new ArrayList<>(backChannelTokenDeliveryModes.size());
                        
                        for (BackChannelTokenDeliveryMode mode: backChannelTokenDeliveryModes) {
                                if (mode != null) {
                                        stringList.add(mode.getValue());
                                }
                        }
                        
                        o.put("backchannel_token_delivery_modes_supported", stringList);
                }
                
                if (backChannelAuthRequestJWSAlgs != null) {
                        
                        stringList = new ArrayList<>(backChannelAuthRequestJWSAlgs.size());
                        
                        for (JWSAlgorithm alg : backChannelAuthRequestJWSAlgs) {
                                if (alg != null) {
                                        stringList.add(alg.getName());
                                }
                        }
                        
                        o.put("backchannel_authentication_request_signing_alg_values_supported", stringList);
                }
                
                if (backChannelUserCodeSupported) {
                        o.put("backchannel_user_code_parameter_supported", true);
                }
                
                
                // Prompt=create
                if (promptTypes != null) {
                        stringList = new ArrayList<>(promptTypes.size());
                        for (Prompt.Type type: promptTypes) {
                                stringList.add(type.toString());
                        }
                        o.put("prompt_values_supported", stringList);
                }
                
                // OIDC Federation 1.0
                
                if (organizationName != null) {
                        o.put("organization_name", organizationName);
                }
                
                if (CollectionUtils.isNotEmpty(clientRegistrationTypes)) {
                        
                        o.put("client_registration_types_supported", Identifier.toStringList(clientRegistrationTypes));
                        
                        if (jwkSet != null) {
                                o.put("jwks", JSONObjectUtils.toJSONObject(jwkSet.toPublicJWKSet())); // prevent private keys from leaking
                        } else if (signedJWKSetURI != null) {
                                o.put("signed_jwks_uri", signedJWKSetURI.toString());
                        }
                        
                        if (clientRegistrationTypes.contains(ClientRegistrationType.AUTOMATIC) && MapUtils.isNotEmpty(clientRegistrationAuthMethods)) {
                                JSONObject map = new JSONObject();
                                for (Map.Entry<EndpointName,List<ClientAuthenticationMethod>> en: getClientRegistrationAuthnMethods().entrySet()) {
                                        List<String> methodNames = new LinkedList<>();
                                        for (ClientAuthenticationMethod method: en.getValue()) {
                                                methodNames.add(method.getValue());
                                        }
                                        map.put(en.getKey().getValue(), methodNames);
                                }
                                o.put("request_authentication_methods_supported", map);
                        }
                        
                        if (clientRegistrationTypes.contains(ClientRegistrationType.AUTOMATIC) && CollectionUtils.isNotEmpty(clientRegistrationAuthJWSAlgs)) {
                                
                                stringList = new ArrayList<>(clientRegistrationAuthJWSAlgs.size());
                                
                                for (JWSAlgorithm alg: clientRegistrationAuthJWSAlgs)
                                        stringList.add(alg.getName());
                                
                                o.put("request_authentication_signing_alg_values_supported", stringList);
                        }
                        
                        if (clientRegistrationTypes.contains(ClientRegistrationType.EXPLICIT) && federationRegistrationEndpoint != null) {
                                o.put("federation_registration_endpoint", federationRegistrationEndpoint.toString());
                        } else {
                                o.remove("federation_registration_endpoint");
                        }
                }

                // Append any custom (not registered) parameters
                o.putAll(customParameters);
                
                return o;
        }
        
        
        /**
         * Parses an OAuth 2.0 Authorisation Server metadata from the specified
         * JSON object.
         *
         * @param jsonObject The JSON object to parse. Must not be
         *                   {@code null}.
         *
         * @return The OAuth 2.0 Authorisation Server metadata.
         *
         * @throws ParseException If the JSON object couldn't be parsed to an
         *                        OAuth 2.0 Authorisation Server metadata.
         */
        public static AuthorizationServerMetadata parse(final JSONObject jsonObject)
                throws ParseException {
                
                // Parse issuer and subject_types_supported first
                
                Issuer issuer = new Issuer(JSONObjectUtils.getURI(jsonObject, "issuer").toString());

                AuthorizationServerEndpointMetadata asEndpoints = AuthorizationServerEndpointMetadata.parse(jsonObject);
                
                AuthorizationServerMetadata as;
                
                try {
                        as = new AuthorizationServerMetadata(issuer); // validates issuer syntax
                } catch (IllegalArgumentException e) {
                        throw new ParseException(e.getMessage(), e);
                }
                
                // Endpoints
                as.setAuthorizationEndpointURI(asEndpoints.getAuthorizationEndpointURI());
                as.setTokenEndpointURI(asEndpoints.getTokenEndpointURI());
                as.setRegistrationEndpointURI(asEndpoints.getRegistrationEndpointURI());
                as.setIntrospectionEndpointURI(asEndpoints.getIntrospectionEndpointURI());
                as.setRevocationEndpointURI(asEndpoints.getRevocationEndpointURI());
                as.setRequestObjectEndpoint(asEndpoints.getRequestObjectEndpoint());
                as.setPushedAuthorizationRequestEndpointURI(asEndpoints.getPushedAuthorizationRequestEndpointURI());
                as.setDeviceAuthorizationEndpointURI(asEndpoints.getDeviceAuthorizationEndpointURI());
                as.setBackChannelAuthenticationEndpointURI(asEndpoints.getBackChannelAuthenticationEndpointURI());
                as.jwkSetURI = JSONObjectUtils.getURI(jsonObject, "jwks_uri", null);
                
                // AS capabilities
                if (jsonObject.get("scopes_supported") != null) {
                        
                        as.scope = new Scope();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "scopes_supported")) {
                                
                                if (v != null)
                                        as.scope.add(new Scope.Value(v));
                        }
                }
                
                if (jsonObject.get("response_types_supported") != null) {
                        
                        as.rts = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "response_types_supported")) {
                                
                                if (v != null)
                                        as.rts.add(ResponseType.parse(v));
                        }
                }
                
                if (jsonObject.get("response_modes_supported") != null) {
                        
                        as.rms = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "response_modes_supported")) {
                                
                                if (v != null)
                                        as.rms.add(new ResponseMode(v));
                        }
                }
                
                if (jsonObject.get("grant_types_supported") != null) {
                        
                        as.gts = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "grant_types_supported")) {
                                
                                if (v != null)
                                        as.gts.add(GrantType.parse(v));
                        }
                }
                
                if (jsonObject.get("code_challenge_methods_supported") != null) {
                        
                        as.codeChallengeMethods = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "code_challenge_methods_supported")) {
                                
                                if (v != null)
                                        as.codeChallengeMethods.add(CodeChallengeMethod.parse(v));
                        }
                }
                
                if (jsonObject.get("token_endpoint_auth_methods_supported") != null) {
                        
                        as.tokenEndpointAuthMethods = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "token_endpoint_auth_methods_supported")) {
                                
                                if (v != null)
                                        as.tokenEndpointAuthMethods.add(ClientAuthenticationMethod.parse(v));
                        }
                }
                
                if (jsonObject.get("token_endpoint_auth_signing_alg_values_supported") != null) {
                        
                        as.tokenEndpointJWSAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "token_endpoint_auth_signing_alg_values_supported")) {
                                
                                if (v != null && v.equals(Algorithm.NONE.getName()))
                                        throw new ParseException("The none algorithm is not accepted");
                                
                                if (v != null)
                                        as.tokenEndpointJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                if (jsonObject.get("introspection_endpoint_auth_methods_supported") != null) {
                        
                        as.introspectionEndpointAuthMethods = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "introspection_endpoint_auth_methods_supported")) {
                                
                                if (v != null)
                                        as.introspectionEndpointAuthMethods.add(ClientAuthenticationMethod.parse(v));
                        }
                }
                
                if (jsonObject.get("introspection_endpoint_auth_signing_alg_values_supported") != null) {
                        
                        as.introspectionEndpointJWSAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "introspection_endpoint_auth_signing_alg_values_supported")) {
                                
                                if (v != null && v.equals(Algorithm.NONE.getName()))
                                        throw new ParseException("The none algorithm is not accepted");
                                
                                if (v != null)
                                        as.introspectionEndpointJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                if (jsonObject.get("revocation_endpoint_auth_methods_supported") != null) {
                        
                        as.revocationEndpointAuthMethods = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "revocation_endpoint_auth_methods_supported")) {
                                
                                if (v != null)
                                        as.revocationEndpointAuthMethods.add(ClientAuthenticationMethod.parse(v));
                        }
                }
                
                if (jsonObject.get("revocation_endpoint_auth_signing_alg_values_supported") != null) {
                        
                        as.revocationEndpointJWSAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "revocation_endpoint_auth_signing_alg_values_supported")) {
                                
                                if (v != null && v.equals(Algorithm.NONE.getName()))
                                        throw new ParseException("The none algorithm is not accepted");
                                
                                if (v != null)
                                        as.revocationEndpointJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                
                // Request object
                if (jsonObject.get("request_object_signing_alg_values_supported") != null) {
                        
                        as.requestObjectJWSAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "request_object_signing_alg_values_supported")) {
                                
                                if (v != null)
                                        as.requestObjectJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                
                if (jsonObject.get("request_object_encryption_alg_values_supported") != null) {
                        
                        as.requestObjectJWEAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "request_object_encryption_alg_values_supported")) {
                                
                                if (v != null)
                                        as.requestObjectJWEAlgs.add(JWEAlgorithm.parse(v));
                        }
                }
                
                
                if (jsonObject.get("request_object_encryption_enc_values_supported") != null) {
                        
                        as.requestObjectJWEEncs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "request_object_encryption_enc_values_supported")) {
                                
                                if (v != null)
                                        as.requestObjectJWEEncs.add(EncryptionMethod.parse(v));
                        }
                }
                
                
                // Misc
                
                if (jsonObject.get("ui_locales_supported") != null) {
                        
                        as.uiLocales = new ArrayList<>();
                        
                        for (String v : JSONObjectUtils.getStringArray(jsonObject, "ui_locales_supported")) {
                                
                                if (v != null) {
                                        
                                        try {
                                                as.uiLocales.add(LangTag.parse(v));
                                                
                                        } catch (LangTagException e) {
                                                
                                                throw new ParseException("Invalid ui_locales_supported field: " + e.getMessage(), e);
                                        }
                                }
                        }
                }
                
                if (jsonObject.get("service_documentation") != null) {
                        try {
                                as.setServiceDocsURI(JSONObjectUtils.getURI(jsonObject, "service_documentation"));
                        } catch (IllegalArgumentException e) {
                                throw new ParseException("Illegal service_documentation parameter: " + e.getMessage());
                        }
                }
                
                if (jsonObject.get("op_policy_uri") != null) {
                        try {
                                as.setPolicyURI(JSONObjectUtils.getURI(jsonObject, "op_policy_uri"));
                        } catch (IllegalArgumentException e) {
                                throw new ParseException("Illegal op_policy_uri parameter: " + e.getMessage());
                        }
                }
                
                if (jsonObject.get("op_tos_uri") != null) {
                        try {
                                as.setTermsOfServiceURI(JSONObjectUtils.getURI(jsonObject, "op_tos_uri"));
                        } catch (IllegalArgumentException e) {
                                throw new ParseException("Illegal op_tos_uri parameter: " + e.getMessage());
                        }
                }
                
                if (jsonObject.get("request_parameter_supported") != null)
                        as.requestParamSupported = JSONObjectUtils.getBoolean(jsonObject, "request_parameter_supported");
                
                if (jsonObject.get("request_uri_parameter_supported") != null)
                        as.requestURIParamSupported = JSONObjectUtils.getBoolean(jsonObject, "request_uri_parameter_supported");
                
                if (jsonObject.get("require_request_uri_registration") != null)
                        as.requireRequestURIReg = JSONObjectUtils.getBoolean(jsonObject, "require_request_uri_registration");
                
                if (jsonObject.get("authorization_response_iss_parameter_supported") != null)
                        as.authzResponseIssParameterSupported = JSONObjectUtils.getBoolean(jsonObject, "authorization_response_iss_parameter_supported");
                
                if (jsonObject.get("mtls_endpoint_aliases") != null)
                        as.mtlsEndpointAliases = AuthorizationServerEndpointMetadata.parse(JSONObjectUtils.getJSONObject(jsonObject, "mtls_endpoint_aliases"));
                
                if (jsonObject.get("tls_client_certificate_bound_access_tokens") != null)
                        as.tlsClientCertificateBoundAccessTokens = JSONObjectUtils.getBoolean(jsonObject, "tls_client_certificate_bound_access_tokens");
                
                // DPoP
                if (jsonObject.get("dpop_signing_alg_values_supported") != null)  {
                        
                        as.dPoPJWSAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "dpop_signing_alg_values_supported")) {
                                
                                if (v != null)
                                        as.dPoPJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                // JARM
                if (jsonObject.get("authorization_signing_alg_values_supported") != null) {
                        
                        as.authzJWSAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "authorization_signing_alg_values_supported")) {
                                
                                if (v != null)
                                        as.authzJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                
                if (jsonObject.get("authorization_encryption_alg_values_supported") != null) {
                        
                        as.authzJWEAlgs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "authorization_encryption_alg_values_supported")) {
                                
                                if (v != null)
                                        as.authzJWEAlgs.add(JWEAlgorithm.parse(v));
                        }
                }
                
                
                if (jsonObject.get("authorization_encryption_enc_values_supported") != null) {
                        
                        as.authzJWEEncs = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "authorization_encryption_enc_values_supported")) {
                                
                                if (v != null)
                                        as.authzJWEEncs.add(EncryptionMethod.parse(v));
                        }
                }
                
                // PAR
                if (jsonObject.get("require_pushed_authorization_requests") != null) {
                        as.requiresPushedAuthorizationRequests(JSONObjectUtils.getBoolean(jsonObject, "require_pushed_authorization_requests"));
                }

                // RAR
                if (jsonObject.get("authorization_details_types_supported") != null) {

                        as.authzTypes = new ArrayList<>();

                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "authorization_details_types_supported")) {

                                if (StringUtils.isNotBlank(v)) {
                                        as.authzTypes.add(new AuthorizationType(v));
                                }
                        }
                }
                
                // Incremental authz
                if (jsonObject.get("incremental_authz_types_supported") != null) {
                        
                        as.incrementalAuthzTypes = new ArrayList<>();
                        
                        for (String v: JSONObjectUtils.getStringArray(jsonObject, "incremental_authz_types_supported")) {
                                
                                if (v != null) {
                                        ClientType clientType;
                                        try {
                                                clientType = ClientType.valueOf(v.toUpperCase());
                                        } catch (IllegalArgumentException e) {
                                                throw new ParseException("Illegal client type in incremental_authz_types_supported field: " + v);
                                        }
                                        as.incrementalAuthzTypes.add(clientType);
                                }
                        }
                }
                
                // CIBA
                if (jsonObject.get("backchannel_token_delivery_modes_supported") != null) {
                        
                        as.backChannelTokenDeliveryModes = new ArrayList<>();

                        for (String v : JSONObjectUtils.getStringArray(jsonObject, "backchannel_token_delivery_modes_supported")) {

                                if (v != null)
                                        as.backChannelTokenDeliveryModes.add(BackChannelTokenDeliveryMode.parse(v));
                        }
                }

                if (jsonObject.get("backchannel_authentication_request_signing_alg_values_supported") != null) {
                        
                        as.backChannelAuthRequestJWSAlgs = new ArrayList<>();

                        for (String v : JSONObjectUtils.getStringArray(jsonObject, "backchannel_authentication_request_signing_alg_values_supported")) {

                                if (v != null)
                                        as.backChannelAuthRequestJWSAlgs.add(JWSAlgorithm.parse(v));
                        }
                }
                
                if (jsonObject.get("backchannel_user_code_parameter_supported") != null) {
                        as.backChannelUserCodeSupported = JSONObjectUtils.getBoolean(jsonObject, "backchannel_user_code_parameter_supported");
                }
                
                // prompt=create
                if (jsonObject.get("prompt_values_supported") != null) {
                        
                        as.promptTypes = new ArrayList<>();
                        for (String v: JSONObjectUtils.getStringList(jsonObject, "prompt_values_supported")) {
                                
                                if (v != null)
                                        as.promptTypes.add(Prompt.Type.parse(v));
                        }
                }
                
                // OIDC Federation 1.0
                if (jsonObject.get("client_registration_types_supported") != null) {
                        
                        as.clientRegistrationTypes = new LinkedList<>();
                        for (String v : JSONObjectUtils.getStringList(jsonObject, "client_registration_types_supported")) {
                                as.clientRegistrationTypes.add(new ClientRegistrationType(v));
                        }
                        
                        if (jsonObject.get("jwks") != null) {
                                try {
                                        as.jwkSet = JWKSet.parse(JSONObjectUtils.getJSONObject(jsonObject, "jwks"));
                                } catch (java.text.ParseException e) {
                                        throw new ParseException(e.getMessage(), e);
                                }
                        }
                        
                        as.signedJWKSetURI = JSONObjectUtils.getURI(jsonObject, "signed_jwks_uri", null);
                        
                        if (jsonObject.get("request_authentication_methods_supported") != null) {
                                Map<EndpointName, List<ClientAuthenticationMethod>> requestAuthMethods = new HashMap<>();
                                JSONObject spec = JSONObjectUtils.getJSONObject(jsonObject, "request_authentication_methods_supported");
                                // authorization_endpoint or RAR
                                for (String endpointName : spec.keySet()) {
                                        List<String> methodNames = JSONObjectUtils.getStringList(spec, endpointName, Collections.<String>emptyList());
                                        List<ClientAuthenticationMethod> authMethods = new LinkedList<>();
                                        for (String name : methodNames) {
                                                authMethods.add(ClientAuthenticationMethod.parse(name));
                                        }
                                        requestAuthMethods.put(new EndpointName(endpointName), authMethods);
                                }
                                as.setClientRegistrationAuthnMethods(requestAuthMethods);
                        }
                        
                        if (jsonObject.get("request_authentication_signing_alg_values_supported") != null) {
                                as.clientRegistrationAuthJWSAlgs = new ArrayList<>();
                                
                                for (String v : JSONObjectUtils.getStringArray(jsonObject, "request_authentication_signing_alg_values_supported")) {
                                        
                                        if (v != null)
                                                as.clientRegistrationAuthJWSAlgs.add(JWSAlgorithm.parse(v));
                                }
                        }
                        
                        as.federationRegistrationEndpoint = JSONObjectUtils.getURI(jsonObject, "federation_registration_endpoint", null);
                }
                
                as.organizationName = JSONObjectUtils.getString(jsonObject, "organization_name", null);
                
                // Parse custom (not registered) parameters
                JSONObject customParams = new JSONObject(jsonObject);
                customParams.keySet().removeAll(REGISTERED_PARAMETER_NAMES);
                for (Map.Entry<String,Object> customEntry: customParams.entrySet()) {
                        as.setCustomParameter(customEntry.getKey(), customEntry.getValue());
                }
                
                return as;
        }
        
        
        /**
         * Parses an OAuth 2.0 Authorisation Server metadata from the specified
         * JSON object string.
         *
         * @param s The JSON object sting to parse. Must not be {@code null}.
         *
         * @return The OAuth 2.0 Authorisation Server metadata.
         *
         * @throws ParseException If the JSON object string couldn't be parsed
         *                        to an OAuth 2.0 Authorisation Server
         *                        metadata.
         */
        public static AuthorizationServerMetadata parse(final String s)
                throws ParseException {
                
                return parse(JSONObjectUtils.parse(s));
        }
        
        
        /**
         * Resolves OAuth 2.0 authorisation server metadata URL from the
         * specified issuer identifier.
         *
         * @param issuer The issuer identifier. Must represent a valid HTTPS or
         *               HTTP URL. Must not be {@code null}.
         *
         * @return The OAuth 2.0 authorisation server metadata URL.
         *
         * @throws GeneralException If the issuer identifier is invalid.
         */
        public static URL resolveURL(final Issuer issuer)
                throws GeneralException {
                
                try {
                        URL issuerURL = new URL(issuer.getValue());
                        
                        // Validate but don't insist on HTTPS
                        if (issuerURL.getQuery() != null && ! issuerURL.getQuery().trim().isEmpty()) {
                                throw new GeneralException("The issuer identifier must not contain a query component");
                        }
                        
                        if (issuerURL.getPath() != null && issuerURL.getPath().endsWith("/")) {
                                return new URL(issuerURL + ".well-known/oauth-authorization-server");
                        } else {
                                return new URL(issuerURL + "/.well-known/oauth-authorization-server");
                        }
                        
                } catch (MalformedURLException e) {
                        throw new GeneralException("The issuer identifier doesn't represent a valid URL: " + e.getMessage(), e);
                }
        }
        
        
        /**
         * Resolves OAuth 2.0 authorisation server metadata from the specified
         * issuer identifier. The metadata is downloaded by HTTP GET from
         * {@code [issuer-url]/.well-known/oauth-authorization-server}.
         *
         * @param issuer The issuer identifier. Must represent a valid HTTPS or
         *               HTTP URL. Must not be {@code null}.
         *
         * @return The OAuth 2.0 authorisation server metadata.
         *
         * @throws GeneralException If the issuer identifier or the downloaded
         *                          metadata are invalid.
         * @throws IOException      On a HTTP exception.
         */
        public static AuthorizationServerMetadata resolve(final Issuer issuer)
                throws GeneralException, IOException {
                
                return resolve(issuer, 0, 0);
        }
        
        
        /**
         * Resolves OAuth 2.0 authorisation server metadata from the specified
         * issuer identifier. The metadata is downloaded by HTTP GET from
         * {@code [issuer-url]/.well-known/oauth-authorization-server}.
         *
         * @param issuer         The issuer identifier. Must represent a valid
         *                       HTTPS or HTTP URL. Must not be {@code null}.
         * @param connectTimeout The HTTP connect timeout, in milliseconds.
         *                       Zero implies no timeout. Must not be negative.
         * @param readTimeout    The HTTP response read timeout, in
         *                       milliseconds. Zero implies no timeout. Must
         *                       not be negative.
         *
         * @return The OAuth 2.0 authorisation server metadata.
         *
         * @throws GeneralException If the issuer identifier or the downloaded
         *                          metadata are invalid.
         * @throws IOException      On a HTTP exception.
         */
        public static AuthorizationServerMetadata resolve(final Issuer issuer,
                                                          final int connectTimeout,
                                                          final int readTimeout)
                throws GeneralException, IOException {
                
                HTTPRequestConfigurator requestConfigurator = new HTTPRequestConfigurator() {
                        @Override
                        public void configure(HTTPRequest httpRequest) {
                                httpRequest.setConnectTimeout(connectTimeout);
                                httpRequest.setReadTimeout(readTimeout);
                        }
                };
                
                return resolve(issuer, requestConfigurator);
        }
        
        
        /**
         * Resolves OAuth 2.0 authorisation server metadata from the specified
         * issuer identifier. The metadata is downloaded by HTTP GET from
         * {@code [issuer-url]/.well-known/oauth-authorization-server}, using
         * the specified HTTP request configurator.
         *
         * @param issuer              The issuer identifier. Must represent a
         *                            valid HTTPS or HTTP URL. Must not be
         *                            {@code null}.
         * @param requestConfigurator An {@link HTTPRequestConfigurator}
         *                            instance to perform additional
         *                            {@link HTTPRequest} configuration to
         *                            fetch the OpenID Provider metadata. Must
         *                            not be {@code null}.
         *
         * @return The OAuth 2.0 authorisation server metadata.
         *
         * @throws GeneralException If the issuer identifier or the downloaded
         *                          metadata are invalid.
         * @throws IOException      On a HTTP exception.
         */
        public static AuthorizationServerMetadata resolve(final Issuer issuer,
                                                          final HTTPRequestConfigurator requestConfigurator)
                throws GeneralException, IOException {
                
                URL configURL = resolveURL(issuer);
                
                HTTPRequest httpRequest = new HTTPRequest(HTTPRequest.Method.GET, configURL);
                requestConfigurator.configure(httpRequest);
                
                HTTPResponse httpResponse = httpRequest.send();
                
                if (httpResponse.getStatusCode() != 200) {
                        throw new IOException("Couldn't download OAuth 2.0 Authorization Server metadata from " + configURL +
                                ": Status code " + httpResponse.getStatusCode());
                }
                
                JSONObject jsonObject = httpResponse.getContentAsJSONObject();
                
                AuthorizationServerMetadata as = AuthorizationServerMetadata.parse(jsonObject);
                
                if (! issuer.equals(as.issuer)) {
                        throw new GeneralException("The returned issuer doesn't match the expected: " + as.getIssuer());
                }
                
                return as;
        }
}