feat: relax StrictOidcDiscoveryMetadataPolicy and add Dynamic Client Registration middleware (RFC 7591)

CHANGELOG.md

@@ -9,6 +9,8 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * Add client component for building MCP clients
 * Add `Builder::setReferenceHandler()` to allow custom `ReferenceHandlerInterface` implementations (e.g. authorization decorators)
 * Add elicitation enum schema types per SEP-1330: `TitledEnumSchemaDefinition`, `MultiSelectEnumSchemaDefinition`, `TitledMultiSelectEnumSchemaDefinition`
+* Allow `StrictOidcDiscoveryMetadataPolicy` to accept metadata without `code_challenge_methods_supported` (defaults to S256 downstream)
+* Add OAuth 2.0 Dynamic Client Registration middleware (RFC 7591)
 
 0.4.0
 -----

examples/server/oauth-microsoft/README.md

@@ -198,8 +198,9 @@ Microsoft's JWKS endpoint is public. Ensure your container can reach:
 
 ### `code_challenge_methods_supported` missing in discovery metadata
 
-This example configures `OidcDiscovery` with `MicrosoftOidcMetadataPolicy`, so this
-field can be missing or malformed and will not fail discovery.
+The default `StrictOidcDiscoveryMetadataPolicy` accepts metadata without `code_challenge_methods_supported`
+(defaults to S256 downstream). The `MicrosoftOidcMetadataPolicy` in this example demonstrates
+how to implement a custom policy via `OidcDiscoveryMetadataPolicyInterface`.
 
 ### Graph API errors
 

src/Exception/ClientRegistrationException.php

@@ -0,0 +1,16 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Exception;
+
+final class ClientRegistrationException extends \RuntimeException implements ExceptionInterface
+{
+}

src/Server/Transport/Http/Middleware/ClientRegistrationMiddleware.php

@@ -0,0 +1,140 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Server\Transport\Http\Middleware;
+
+use Http\Discovery\Psr17FactoryDiscovery;
+use Mcp\Exception\ClientRegistrationException;
+use Mcp\Exception\InvalidArgumentException;
+use Mcp\Server\Transport\Http\OAuth\ClientRegistrarInterface;
+use Psr\Http\Message\ResponseFactoryInterface;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Message\StreamFactoryInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+/**
+ * OAuth 2.0 Dynamic Client Registration (RFC 7591) middleware.
+ *
+ * Handles POST /register requests by delegating to a ClientRegistrarInterface
+ * and enriches /.well-known/oauth-authorization-server responses with the
+ * registration_endpoint.
+ */
+final class ClientRegistrationMiddleware implements MiddlewareInterface
+{
+    private const REGISTRATION_PATH = '/register';
+
+    private ResponseFactoryInterface $responseFactory;
+    private StreamFactoryInterface $streamFactory;
+
+    public function __construct(
+        private readonly ClientRegistrarInterface $registrar,
+        private readonly string $localBaseUrl,
+        ?ResponseFactoryInterface $responseFactory = null,
+        ?StreamFactoryInterface $streamFactory = null,
+    ) {
+        if ('' === trim($localBaseUrl)) {
+            throw new InvalidArgumentException('The $localBaseUrl must not be empty.');
+        }
+
+        $this->responseFactory = $responseFactory ?? Psr17FactoryDiscovery::findResponseFactory();
+        $this->streamFactory = $streamFactory ?? Psr17FactoryDiscovery::findStreamFactory();
+    }
+
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        $path = $request->getUri()->getPath();
+
+        if ('POST' === $request->getMethod() && self::REGISTRATION_PATH === $path) {
+            return $this->handleRegistration($request);
+        }
+
+        $response = $handler->handle($request);
+
+        if ('GET' === $request->getMethod() && '/.well-known/oauth-authorization-server' === $path) {
+            return $this->enrichAuthServerMetadata($response);
+        }
+
+        return $response;
+    }
+
+    private function handleRegistration(ServerRequestInterface $request): ResponseInterface
+    {
+        $body = $request->getBody()->__toString();
+        $data = json_decode($body, true);
+
+        if (!\is_array($data)) {
+            return $this->jsonResponse(400, [
+                'error' => 'invalid_client_metadata',
+                'error_description' => 'Request body must be valid JSON.',
+            ]);
+        }
+
+        try {
+            $result = $this->registrar->register($data);
+        } catch (ClientRegistrationException $e) {
+            return $this->jsonResponse(400, [
+                'error' => 'invalid_client_metadata',
+                'error_description' => $e->getMessage(),
+            ]);
+        }
+
+        return $this->jsonResponse(201, $result);
+    }
+
+    private function enrichAuthServerMetadata(ResponseInterface $response): ResponseInterface
+    {
+        if (200 !== $response->getStatusCode()) {
+            return $response;
+        }
+
+        $stream = $response->getBody();
+
+        if ($stream->isSeekable()) {
+            $stream->rewind();
+        }
+
+        $metadata = json_decode($stream->__toString(), true);
+
+        if (!\is_array($metadata)) {
+            return $response;
+        }
+
+        $metadata['registration_endpoint'] = rtrim($this->localBaseUrl, '/').self::REGISTRATION_PATH;
+
+        return $this->jsonResponse(200, $metadata, [
+            'Cache-Control' => $response->getHeaderLine('Cache-Control'),
+        ]);
+    }
+
+    /**
+     * @param array<string, mixed>  $data
+     * @param array<string, string> $extraHeaders
+     */
+    private function jsonResponse(int $status, array $data, array $extraHeaders = []): ResponseInterface
+    {
+        $response = $this->responseFactory
+            ->createResponse($status)
+            ->withHeader('Content-Type', 'application/json')
+            ->withBody($this->streamFactory->createStream(
+                json_encode($data, \JSON_THROW_ON_ERROR | \JSON_UNESCAPED_SLASHES),
+            ));
+
+        foreach ($extraHeaders as $name => $value) {
+            if ('' !== $value) {
+                $response = $response->withHeader($name, $value);
+            }
+        }
+
+        return $response;
+    }
+}

src/Server/Transport/Http/OAuth/ClientRegistrarInterface.php

@@ -0,0 +1,42 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Server\Transport\Http\OAuth;
+
+use Mcp\Exception\ClientRegistrationException;
+
+/**
+ * Interface for OAuth 2.0 Dynamic Client Registration (RFC 7591).
+ *
+ * Implementations are responsible for persisting client credentials and
+ * returning a registration response as defined in RFC 7591 Section 3.2.
+ *
+ * @see https://datatracker.ietf.org/doc/html/rfc7591
+ */
+interface ClientRegistrarInterface
+{
+    /**
+     * Registers a new OAuth 2.0 client.
+     *
+     * The registration request contains metadata fields as defined in RFC 7591
+     * Section 2 (e.g. redirect_uris, client_name, token_endpoint_auth_method).
+     *
+     * The returned array MUST include at least "client_id" and should include
+     * "client_secret" when the token endpoint auth method requires one.
+     *
+     * @param array<string, mixed> $registrationRequest Client metadata from the registration request body
+     *
+     * @return array<string, mixed> Registration response including client_id and optional client_secret
+     *
+     * @throws ClientRegistrationException If registration fails (e.g. invalid metadata, storage error)
+     */
+    public function register(array $registrationRequest): array;
+}

src/Server/Transport/Http/OAuth/StrictOidcDiscoveryMetadataPolicy.php

@@ -28,19 +28,20 @@ public function isValid(mixed $metadata): bool
             || '' === trim($metadata['token_endpoint'])
             || !\is_string($metadata['jwks_uri'])
             || '' === trim($metadata['jwks_uri'])
-            || !isset($metadata['code_challenge_methods_supported'])
         ) {
             return false;
         }
 
-        if (!\is_array($metadata['code_challenge_methods_supported']) || [] === $metadata['code_challenge_methods_supported']) {
-            return false;
-        }
-
-        foreach ($metadata['code_challenge_methods_supported'] as $method) {
-            if (!\is_string($method) || '' === trim($method)) {
+        if (isset($metadata['code_challenge_methods_supported'])) {
+            if (!\is_array($metadata['code_challenge_methods_supported']) || [] === $metadata['code_challenge_methods_supported']) {
                 return false;
             }
+
+            foreach ($metadata['code_challenge_methods_supported'] as $method) {
+                if (!\is_string($method) || '' === trim($method)) {
+                    return false;
+                }
+            }
         }
 
         return true;