fix: address MR review comments for ClientRegistration

- Use Mcp\Exception\InvalidArgumentException instead of global \InvalidArgumentException
- Add interface documentation for ClientRegistrarInterface with RFC 7591 references

Author: simonchrz

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

@@ -13,6 +13,7 @@
 
 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;
@@ -42,7 +43,7 @@ public function __construct(
         ?StreamFactoryInterface $streamFactory = null,
     ) {
         if ('' === trim($localBaseUrl)) {
-            throw new \InvalidArgumentException('The $localBaseUrl must not be empty.');
+            throw new InvalidArgumentException('The $localBaseUrl must not be empty.');
         }
 
         $this->responseFactory = $responseFactory ?? Psr17FactoryDiscovery::findResponseFactory();

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

@@ -15,15 +15,28 @@
 
 /**
  * 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
 {
     /**
-     * @param array<string, mixed> $registrationRequest
+     * 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>
+     * @return array<string, mixed> Registration response including client_id and optional client_secret
      *
-     * @throws ClientRegistrationException
+     * @throws ClientRegistrationException If registration fails (e.g. invalid metadata, storage error)
      */
     public function register(array $registrationRequest): array;
 }

tests/Unit/Server/Transport/Http/Middleware/ClientRegistrationMiddlewareTest.php

@@ -12,6 +12,7 @@
 namespace Mcp\Tests\Unit\Server\Transport\Http\Middleware;
 
 use Mcp\Exception\ClientRegistrationException;
+use Mcp\Exception\InvalidArgumentException;
 use Mcp\Server\Transport\Http\Middleware\ClientRegistrationMiddleware;
 use Mcp\Server\Transport\Http\OAuth\ClientRegistrarInterface;
 use Nyholm\Psr7\Factory\Psr17Factory;
@@ -165,7 +166,7 @@ public function testNonMatchingRoutePassesThrough(): void
     #[TestDox('constructor rejects empty localBaseUrl')]
     public function testConstructorRejectsEmptyBaseUrl(): void
     {
-        $this->expectException(\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         new ClientRegistrationMiddleware(
             $this->createStub(ClientRegistrarInterface::class),