OAuth authentication request fails with MS Entra-ID

[mbuchberger1967]

Hi, I just checked out the 0.3.0-preview.3 release and I modified the ProtectedMCPServer and ProtectedMCPClient samples to use MS Entra-ID as OAUTH server (see code snippets below):
The URL that is created by the mcp server for starting the OAUTH flow looks like this:

https://login.microsoftonline.com/<tenant-id>/oauth2/v2.0/authorize?client_id=xxxxx&redirect_uri=http%3a%2f%2flocalhost%3a1179%2fcallback&response_type=code&code_challenge=q09KNTJ_gyVsLnvjSSX46MYl_DcPTuNhosF6U5n9KOs&code_challenge_method=S256&resource=http%3a%2f%2flocalhost%3a7077%2f&scope=api%3a%2f%xxxx-xxxxx-xxxxx%2fmcp.tools

This url contains a resource and a scope parameter.
But MS Entra-ID complains about the resource parameter, as in OAuth 2.0 it should be the scope parameter used:
AADSTS901002: The 'resource' request parameter is not supported.

What is your idea or hint to solve this problem?

My changes:
Client: I added the ClientId which I configured in Azure portal

var transport = new SseClientTransport(new()
{
    Endpoint = new Uri(serverUrl),
    Name = "Secure Weather Client",
    OAuth = new()
    {
        ClientName = "ProtectedMcpClient",
        ClientId = "xxxx-xxxxx-xxxx-xxxx",
        RedirectUri = new Uri("http://localhost:1179/callback"),
        AuthorizationRedirectDelegate = HandleAuthorizationUrlAsync,
    }
}, httpClient, consoleLoggerFactory);

Server:
changed the OAuth server url:
var inMemoryOAuthServerUrl = "https://login.microsoftonline.com/<tenant-id>/v2.0";

changed ScopesSupported analog to the Azure Portal definition:
ScopesSupported = ["api://7e7eaf63-375a-4a0d-9872-574fdb5e08d6/mcp.tools"],

Thanks
Markus

[eusebiu]

I get that too! According to https://learn.microsoft.com/en-us/entra/identity-platform/v2-oauth2-auth-code-flow the resource is not part of the request.

I think this part should be as simple as MSAL - on the server just use the existing ASP.NET Authentication & Authorization mechanisms & UX (e.g. [Authorize] attribute with a role over the MCP Server/Tool - e.g. I would like to separate the role of agent/AI vs user roles) and on the client side, simply use MSAL to get the token (e.g. authorization flow, client secret, device code, etc.) and add it to the protocol as we do for HttpClient (Authorization header: Bearer token).

The MCP client should not perform any OAuth functionalities directly like opening the browser, getting the token as there are libraries for that way much better coded/tested.

[eusebiu]

I got it to work (i.e. the authentication) using this workaround (i.e. by removing the resource and adding the grant_type) but I get an exception when creating the MCP client - essentially for the same reason (resource is being sent -

csharp-sdk/src/ModelContextProtocol.Core/Authentication/ClientOAuthProvider.cs

Line 384 in 650df63

["resource"] = protectedResourceMetadata.Resource.ToString(),

).

// on server
services.AddAuthentication(options =>
{
    options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
    options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
})
.AddMcp(options =>
{
    options.ResourceMetadata = new()
    {
        Resource = new Uri("http://localhost:53969/sse"),
        AuthorizationServers = { new Uri("https://login.microsoftonline.com/<tenant>/v2.0") },
        ScopesSupported = ["some_scope"], // from Entra App Registration
        ResourceName = "MCP API",
    };
})
.AddMicrosoftIdentityWebApi(configuration.GetSection("Authentication"));

// in client
var transport = new SseClientTransport(new()
{
    Endpoint = new Uri("http://localhost:53969/sse"),
    Name = "Secure MCP Client",

    OAuth = new()
    {
        ClientName = "API MCP Client",
        ClientId = "xxx",
        RedirectUri = new Uri("http://localhost:8080"), // correct redirect URL from Entra App Registration
        AuthorizationRedirectDelegate = HandleAuthorizationUrlAsync,
    }
}, loggerFactory);

// FAILS HERE - see below
var mcpClient = await McpClientFactory.CreateAsync(
    transport,
	loggerFactory: loggerFactory);

static async Task<string?> HandleAuthorizationUrlAsync(Uri authorizationUrl, Uri redirectUri, CancellationToken cancellationToken)
{
    Console.WriteLine("Starting OAuth authorization flow...");

    // remove 'resource' query parameter if present
    var uriBuilder = new UriBuilder(authorizationUrl);
    var query = HttpUtility.ParseQueryString(uriBuilder.Query);
    query.Remove("resource");
    uriBuilder.Query = query.ToString();

    // add 'grant_type' query parameter if not present
    if (!query.AllKeys.Contains("grant_type"))
    {
        query["grant_type"] = "authorization_code";
        uriBuilder.Query = query.ToString();
    }
    authorizationUrl = uriBuilder.Uri;

    Console.WriteLine($"Opening browser to: {authorizationUrl}");
    // rest of the code
}

Exception:

Listening for OAuth callback on: http://localhost:8080/
Authorization code received successfully.
warn: ModelContextProtocol.Client.SseClientSessionTransport[1753402347]
      Secure  API MCP Client transport message reading failed.
      System.Net.Http.HttpRequestException: Response status code does not indicate success: 400 (Bad Request).
         at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
         at ModelContextProtocol.Authentication.ClientOAuthProvider.FetchTokenAsync(HttpRequestMessage request, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.ExchangeCodeForTokenAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, String authorizationCode, String codeVerifier, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.InitiateAuthorizationCodeFlowAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, CancellationToken cancellationToken)         at ModelContextProtocol.Authentication.ClientOAuthProvider.PerformOAuthAuthorizationAsync(HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.HandleUnauthorizedResponseAsync(String scheme, HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.HandleUnauthorizedResponseAsync(HttpRequestMessage originalRequest, JsonRpcMessage originalJsonRpcMessage, HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.SendAsync(HttpRequestMessage request, JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.SseClientSessionTransport.ReceiveMessagesAsync(CancellationToken cancellationToken)
fail: ModelContextProtocol.Client.SseClientSessionTransport[1985454809]
      Secure  API MCP Client transport connect failed.
      System.Net.Http.HttpRequestException: Response status code does not indicate success: 400 (Bad Request).
         at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
         at ModelContextProtocol.Authentication.ClientOAuthProvider.FetchTokenAsync(HttpRequestMessage request, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.ExchangeCodeForTokenAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, String authorizationCode, String codeVerifier, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.InitiateAuthorizationCodeFlowAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, CancellationToken cancellationToken)         at ModelContextProtocol.Authentication.ClientOAuthProvider.PerformOAuthAuthorizationAsync(HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.HandleUnauthorizedResponseAsync(String scheme, HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.HandleUnauthorizedResponseAsync(HttpRequestMessage originalRequest, JsonRpcMessage originalJsonRpcMessage, HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.SendAsync(HttpRequestMessage request, JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.SseClientSessionTransport.ReceiveMessagesAsync(CancellationToken cancellationToken)
         at ModelContextProtocol.Client.SseClientSessionTransport.ConnectAsync(CancellationToken cancellationToken)
fail: ModelContextProtocol.Client.McpClient[1155727496]
      Secure  API MCP Client client initialization error.
      System.Net.Http.HttpRequestException: Response status code does not indicate success: 400 (Bad Request).
         at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
         at ModelContextProtocol.Authentication.ClientOAuthProvider.FetchTokenAsync(HttpRequestMessage request, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.ExchangeCodeForTokenAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, String authorizationCode, String codeVerifier, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.InitiateAuthorizationCodeFlowAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, CancellationToken cancellationToken)         at ModelContextProtocol.Authentication.ClientOAuthProvider.PerformOAuthAuthorizationAsync(HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.ClientOAuthProvider.HandleUnauthorizedResponseAsync(String scheme, HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.HandleUnauthorizedResponseAsync(HttpRequestMessage originalRequest, JsonRpcMessage originalJsonRpcMessage, HttpResponseMessage response, CancellationToken cancellationToken)
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.SendAsync(HttpRequestMessage request, JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.SseClientSessionTransport.ReceiveMessagesAsync(CancellationToken cancellationToken)
         at ModelContextProtocol.Client.SseClientSessionTransport.CloseAsync()
         at ModelContextProtocol.Client.SseClientSessionTransport.ConnectAsync(CancellationToken cancellationToken)
         at ModelContextProtocol.Client.AutoDetectingClientSessionTransport.InitializeSseTransportAsync(JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.AutoDetectingClientSessionTransport.InitializeSseTransportAsync(JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.AutoDetectingClientSessionTransport.InitializeAsync(JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.AutoDetectingClientSessionTransport.InitializeAsync(JsonRpcMessage message, CancellationToken cancellationToken)
         at ModelContextProtocol.McpSession.SendRequestAsync(JsonRpcRequest request, CancellationToken cancellationToken)
         at ModelContextProtocol.McpEndpointExtensions.SendRequestAsync[TParameters,TResult](IMcpEndpoint endpoint, String method, TParameters parameters, JsonTypeInfo`1 parametersTypeInfo, JsonTypeInfo`1 resultTypeInfo, RequestId requestId, CancellationToken cancellationToken)
         at ModelContextProtocol.Client.McpClient.ConnectAsync(CancellationToken cancellationToken)