mcp: add oauth metadata endpoint (#5579)

internal/mcp/handler_metadata.go

@@ -0,0 +1,129 @@
+package mcp
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"path"
+
+	"github.com/gorilla/mux"
+	"github.com/rs/cors"
+)
+
+// AuthorizationServerMetadata represents the OAuth 2.0 Authorization Server Metadata (RFC 8414).
+// https://datatracker.ietf.org/doc/html/rfc8414#section-2
+type AuthorizationServerMetadata struct {
+	// Issuer is REQUIRED. The authorization server's issuer identifier, a URL using the "https" scheme with no query or fragment.
+	Issuer string `json:"issuer"`
+
+	// AuthorizationEndpoint is the URL of the authorization server's authorization endpoint. REQUIRED unless no grant types use the authorization endpoint.
+	AuthorizationEndpoint string `json:"authorization_endpoint,omitempty"`
+
+	// TokenEndpoint is the URL of the authorization server's token endpoint. REQUIRED unless only the implicit grant type is supported.
+	TokenEndpoint string `json:"token_endpoint,omitempty"`
+
+	// JwksURI is OPTIONAL. URL of the authorization server's JWK Set document.
+	JwksURI string `json:"jwks_uri,omitempty"`
+
+	// RegistrationEndpoint is OPTIONAL. URL of the authorization server's OAuth 2.0 Dynamic Client Registration endpoint.
+	RegistrationEndpoint string `json:"registration_endpoint,omitempty"`
+
+	// ScopesSupported is RECOMMENDED. JSON array of supported OAuth 2.0 "scope" values.
+	ScopesSupported []string `json:"scopes_supported,omitempty"`
+
+	// ResponseTypesSupported is REQUIRED. JSON array of supported OAuth 2.0 "response_type" values.
+	ResponseTypesSupported []string `json:"response_types_supported"`
+
+	// ResponseModesSupported is OPTIONAL. JSON array of supported OAuth 2.0 "response_mode" values. Default: ["query", "fragment"].
+	ResponseModesSupported []string `json:"response_modes_supported,omitempty"`
+
+	// GrantTypesSupported is OPTIONAL. JSON array of supported OAuth 2.0 grant type values. Default: ["authorization_code", "implicit"].
+	GrantTypesSupported []string `json:"grant_types_supported,omitempty"`
+
+	// TokenEndpointAuthMethodsSupported is OPTIONAL. JSON array of client authentication methods supported by the token endpoint. Default: "client_secret_basic".
+	TokenEndpointAuthMethodsSupported []string `json:"token_endpoint_auth_methods_supported,omitempty"`
+
+	// TokenEndpointAuthSigningAlgValuesSupported is OPTIONAL. JSON array of JWS signing algorithms supported by the token endpoint for JWT client authentication.
+	TokenEndpointAuthSigningAlgValuesSupported []string `json:"token_endpoint_auth_signing_alg_values_supported,omitempty"`
+
+	// ServiceDocumentation is OPTIONAL. URL of a page with human-readable information for developers.
+	ServiceDocumentation string `json:"service_documentation,omitempty"`
+
+	// UILocalesSupported is OPTIONAL. JSON array of supported languages and scripts for the UI, as BCP 47 language tags.
+	UILocalesSupported []string `json:"ui_locales_supported,omitempty"`
+
+	// OpPolicyURI is OPTIONAL. URL for the authorization server's policy on client data usage.
+	OpPolicyURI string `json:"op_policy_uri,omitempty"`
+
+	// OpTosURI is OPTIONAL. URL for the authorization server's terms of service.
+	OpTosURI string `json:"op_tos_uri,omitempty"`
+
+	// RevocationEndpoint is OPTIONAL. URL of the authorization server's OAuth 2.0 revocation endpoint.
+	RevocationEndpoint string `json:"revocation_endpoint,omitempty"`
+
+	// RevocationEndpointAuthMethodsSupported is OPTIONAL. JSON array of client authentication methods supported by the revocation endpoint. Default: "client_secret_basic".
+	RevocationEndpointAuthMethodsSupported []string `json:"revocation_endpoint_auth_methods_supported,omitempty"`
+
+	// RevocationEndpointAuthSigningAlgValuesSupported is OPTIONAL. JSON array of JWS signing algorithms supported by the revocation endpoint for JWT client authentication.
+	RevocationEndpointAuthSigningAlgValuesSupported []string `json:"revocation_endpoint_auth_signing_alg_values_supported,omitempty"`
+
+	// IntrospectionEndpoint is OPTIONAL. URL of the authorization server's OAuth 2.0 introspection endpoint.
+	IntrospectionEndpoint string `json:"introspection_endpoint,omitempty"`
+
+	// IntrospectionEndpointAuthMethodsSupported is OPTIONAL. JSON array of client authentication methods supported by the introspection endpoint.
+	IntrospectionEndpointAuthMethodsSupported []string `json:"introspection_endpoint_auth_methods_supported,omitempty"`
+
+	// IntrospectionEndpointAuthSigningAlgValuesSupported is OPTIONAL. JSON array of JWS signing algorithms supported by the introspection endpoint for JWT client authentication.
+	IntrospectionEndpointAuthSigningAlgValuesSupported []string `json:"introspection_endpoint_auth_signing_alg_values_supported,omitempty"`
+
+	// CodeChallengeMethodsSupported is OPTIONAL. JSON array of PKCE code challenge methods supported by this authorization server.
+	CodeChallengeMethodsSupported []string `json:"code_challenge_methods_supported,omitempty"`
+}
+
+func AuthorizationServerMetadataHandler(prefix string) http.HandlerFunc {
+	c := cors.New(cors.Options{
+		AllowedMethods: []string{http.MethodGet, http.MethodOptions},
+		AllowedOrigins: []string{"*"},
+		AllowedHeaders: []string{"mcp-protocol-version"},
+	})
+	r := mux.NewRouter()
+	r.Use(c.Handler)
+	r.Methods(http.MethodGet).HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+
+		meta := getAuthorizationServerMetadata(r.Host, prefix)
+		_ = json.NewEncoder(w).Encode(meta)
+	})
+	r.Methods(http.MethodOptions).HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusNoContent)
+	})
+	return http.HandlerFunc(r.ServeHTTP)
+}
+
+func getAuthorizationServerMetadata(host, prefix string) AuthorizationServerMetadata {
+	baseURL := url.URL{
+		Scheme: "https",
+		Host:   host,
+	}
+	P := func(path string) string {
+		u := baseURL
+		u.Path = path
+		return u.String()
+	}
+
+	return AuthorizationServerMetadata{
+		Issuer:                                 P("/"),
+		ServiceDocumentation:                   "https://pomerium.com/docs",
+		AuthorizationEndpoint:                  P(path.Join(prefix, authorizationEndpoint)),
+		ResponseTypesSupported:                 []string{"code"},
+		CodeChallengeMethodsSupported:          []string{"S256"},
+		TokenEndpoint:                          P(path.Join(prefix, tokenEndpoint)),
+		TokenEndpointAuthMethodsSupported:      []string{"none"},
+		GrantTypesSupported:                    []string{"authorization_code", "refresh_token"},
+		RevocationEndpoint:                     P(path.Join(prefix, revocationEndpoint)),
+		RevocationEndpointAuthMethodsSupported: []string{"client_secret_post"},
+		RegistrationEndpoint:                   P(path.Join(prefix, registerEndpoint)),
+		ScopesSupported:                        []string{"openid", "offline"},
+	}
+}