Not able to authenticate MCP Servers

[pratikgolchha]

Describe the bug
MCP servers are enable with Entra Id auth and when we are getting tools information it is failing to authenticate the MCP servers.
Error : Unable to download OpenID Connect Configuration.

Expected behavior
Authentication should work for MCP servers.

Logs
StatusCode: 500, ReasonPhrase: 'Unable to download OpenID Connect Configuration.'

[PederHP]

Can you give a bit more info? Is this a problem with MCP Servers you have authored using the C# SDK, or third party MCP Servers you are connecting to and authing using and MCP Client Host written using the C# SDK? Do you have a brief code snippet to share?

[pratikgolchha]

MCP servers authored using C# SDK. So basically, these are Custom MCP servers.

[PederHP]

Can you give some more info on how the servers are configured compared to:

https://github.com/modelcontextprotocol/csharp-sdk/blob/main/samples/ProtectedMcpServer/Program.cs

Can you provide a stack trace of where the exception is thrown?

[kimbell]

We are in the same position. I work for a company that uses Entra Id and we are trying to get Visual Studio to talk to a locally developed MCP server . With the Microsoft AI hype train going at full speed and Entra being a mature product, we assumed this would be plain sailing.

After doing some digging, we discovered that MCP uses Dynamic Client Registration. This answer indicates that Entra currently doesn't support this. https://learn.microsoft.com/en-us/answers/questions/5516363/does-entraid-has-a-plan-to-introduce-dynamic-clien

A reference was made to the ProtectedMcpServer setup, so I started digging into that. That uses an OAuth server developed for testing purposes; not something I would want to spin up in a corporate environment.

If Microsoft wants customers to try this out, they need to provide a realistic setup for how to get this working with their own infrastructure. An initial setup doesn't have to be streamlined for ease of setup, but needs to be secure. As it is now, everyone has to try to figure out their own solution. Chances are that some will say "this is is crap" and move on to something else. This type of sentiment may linger for a long time, such as ".NET only runs on Windows"

This AI landscape changes all the time. What doesn't work today works next month. Is there a timeframe for getting this working without having to resort to creative coding? As it currently stands it looks like the marketing team are two releases ahead of the engineering team.

[eduardomb-aw]

ape changes all the time. What doesn't work today works next month. Is there a

Hey @kimbell , the ProtectedMcpServer sample can be used as a starting point to set up a server that authenticates with a real authority like MS Entra. I got that working last week. Here is what the Program.cs looks like (for proof of concept only, not for production use given it exposes secrets):

using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;
using ModelContextProtocol.AspNetCore.Authentication;
using ProtectedMcpServer.Tools;
using System.Net.Http.Headers;
using System.Security.Claims;

var builder = WebApplication.CreateBuilder(args);

var serverUrl = "http://localhost:7071/";

// Microsoft Entra ID configuration
var tenantId = "<your tenant id>";
var clientId = "<your client id>";
var entraAuthorityUrl = $"https://login.microsoftonline.com/{tenantId}/v2.0";

// Add configuration for client secret (needed for On-Behalf-Of flow)
builder.Configuration["AzureAd:ClientSecret"] = "<your client secret>";

builder.Services.AddAuthentication(options =>
{
    options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
    options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
})
.AddJwtBearer(options =>
{
    // Configure to validate tokens from Microsoft Entra ID
    options.Authority = entraAuthorityUrl;
    options.TokenValidationParameters = new TokenValidationParameters
    {
        ValidateIssuer = true,
        ValidateAudience = true,
        ValidateLifetime = true,
        ValidateIssuerSigningKey = true,
        ValidAudiences = new[] { clientId, $"api://{clientId}" },
        ValidIssuers = new[] { 
            entraAuthorityUrl,
            $"https://sts.windows.net/{tenantId}/"
        },
        NameClaimType = ClaimTypes.Name,
        RoleClaimType = ClaimTypes.Role
    };

    options.Events = new JwtBearerEvents
    {
        OnTokenValidated = context =>
        {
            var name = context.Principal?.FindFirstValue("name") ?? 
                      context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
            var upn = context.Principal?.FindFirstValue("upn") ??
                       context.Principal?.FindFirstValue("email") ?? 
                       context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
            var tenantId = context.Principal?.FindFirstValue("tid");
            Console.WriteLine($"Token validated for: {name} ({upn}) from tenant: {tenantId}");
            return Task.CompletedTask;
        },
        OnAuthenticationFailed = context =>
        {
            Console.WriteLine($"Authentication failed: {context.Exception.Message}");
            return Task.CompletedTask;
        },
        OnChallenge = context =>
        {
            Console.WriteLine($"Challenging client to authenticate with Entra ID");
            return Task.CompletedTask;
        }
    };
})
.AddMcp(options =>
{
    options.ResourceMetadata = new()
    {
        Resource = new Uri(serverUrl),
        ResourceDocumentation = new Uri("https://docs.example.com/api/weather"),
        AuthorizationServers = { new Uri($"https://login.microsoftonline.com/{tenantId}/v2.0/") },
        ScopesSupported = [$"api://{clientId}/user_impersonation"], // this is whatever scope you defined in your app reg
    };
});

builder.Services.AddAuthorization();

builder.Services.AddHttpContextAccessor();
builder.Services.AddMcpServer()
    .WithToolsFromAssembly()
    .WithHttpTransport();

// Configure HttpClientFactory for weather.gov API
builder.Services.AddHttpClient("WeatherApi", client =>
{
    client.BaseAddress = new Uri("https://api.weather.gov");
    client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("weather-tool", "1.0"));
});

// Configure HttpClientFactory for Microsoft Graph API
builder.Services.AddHttpClient("GraphApi", client =>
{
    client.BaseAddress = new Uri("https://graph.microsoft.com");
    client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("mcp-server", "1.0"));
});

var app = builder.Build();

app.UseAuthentication();
app.UseAuthorization();

app.MapMcp().RequireAuthorization();

Console.WriteLine($"Starting MCP server with Entra ID authorization at {serverUrl}");
Console.WriteLine($"Using Microsoft Entra ID tenant: {tenantId}");
Console.WriteLine($"Client ID: {clientId}");
Console.WriteLine($"Authority: {entraAuthorityUrl}");
Console.WriteLine($"Protected Resource Metadata URL: {serverUrl}.well-known/oauth-protected-resource");
Console.WriteLine("Press Ctrl+C to stop the server");

app.Run(serverUrl);

And here is GraphTools.cs

using ModelContextProtocol;
using ModelContextProtocol.Server;
using System.ComponentModel;
using System.Net.Http.Headers;
using System.Security.Claims;
using System.Text.Json;

namespace ProtectedMcpServer.Tools;

[McpServerToolType]
public sealed class GraphTools
{
    private readonly IHttpClientFactory _httpClientFactory;
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly IConfiguration _configuration;

    public GraphTools(IHttpClientFactory httpClientFactory, IHttpContextAccessor httpContextAccessor, IConfiguration configuration)
    {
        _httpClientFactory = httpClientFactory;
        _httpContextAccessor = httpContextAccessor;
        _configuration = configuration;
    }

    [McpServerTool, Description("Get a personalized hello message using Microsoft Graph.")]
    public async Task<string> Hello()
    {
        // Get the current user's access token from the HTTP context
        var httpContext = _httpContextAccessor.HttpContext 
            ?? throw new McpException("HTTP context not available");
        
        var authHeader = httpContext.Request.Headers.Authorization.FirstOrDefault();
        if (string.IsNullOrEmpty(authHeader) || !authHeader.StartsWith("Bearer "))
        {
            throw new McpException("No valid bearer token found in request");
        }
        
        var mcpAccessToken = authHeader["Bearer ".Length..];
        
        try
        {
            // Exchange the MCP token for a Microsoft Graph token using On-Behalf-Of flow
            var graphAccessToken = await GetGraphTokenAsync(mcpAccessToken);
            
            // Create HTTP client for Microsoft Graph
            var client = _httpClientFactory.CreateClient("GraphApi");
            
            // Add the Graph access token to the request
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", graphAccessToken);
            
            // Call Microsoft Graph /me endpoint
            var response = await client.GetAsync("/v1.0/me");
            
            if (!response.IsSuccessStatusCode)
            {
                throw new McpException($"Microsoft Graph API call failed: {response.StatusCode} - {await response.Content.ReadAsStringAsync()}");
            }
            
            var jsonContent = await response.Content.ReadAsStringAsync();
            using var document = JsonDocument.Parse(jsonContent);
            var root = document.RootElement;
            
            // Extract the user's display name from the response
            var displayName = root.TryGetProperty("displayName", out var nameElement) 
                ? nameElement.GetString() 
                : null;
            
            // Fallback to other name properties if displayName is not available
            if (string.IsNullOrEmpty(displayName))
            {
                displayName = root.TryGetProperty("givenName", out var givenNameElement)
                    ? givenNameElement.GetString()
                    : root.TryGetProperty("userPrincipalName", out var upnElement)
                        ? upnElement.GetString()?.Split('@')[0] // Take the part before @ for UPN
                        : "User";
            }
            
            return $"Hello, {displayName}!!";
        }
        catch (HttpRequestException ex)
        {
            throw new McpException($"Failed to call Microsoft Graph API: {ex.Message}", ex);
        }
        catch (JsonException ex)
        {
            throw new McpException($"Failed to parse Microsoft Graph API response: {ex.Message}", ex);
        }
    }

    private async Task<string> GetGraphTokenAsync(string mcpAccessToken)
    {
        var tenantId = "<your tenant id>";
        var clientId = "<your client id>";
        var clientSecret = _configuration["AzureAd:ClientSecret"] 
            ?? throw new McpException("Client secret not configured for On-Behalf-Of flow");
        
        var client = _httpClientFactory.CreateClient();
        
        var tokenEndpoint = $"https://login.microsoftonline.com/{tenantId}/oauth2/v2.0/token";
        
        var requestParams = new Dictionary<string, string>
        {
            ["grant_type"] = "urn:ietf:params:oauth:grant-type:jwt-bearer",
            ["client_id"] = clientId,
            ["client_secret"] = clientSecret,
            ["assertion"] = mcpAccessToken,
            ["scope"] = "https://graph.microsoft.com/User.Read",
            ["requested_token_use"] = "on_behalf_of"
        };
        
        var requestContent = new FormUrlEncodedContent(requestParams);
        
        var response = await client.PostAsync(tokenEndpoint, requestContent);
        
        if (!response.IsSuccessStatusCode)
        {
            var errorContent = await response.Content.ReadAsStringAsync();
            throw new McpException($"On-Behalf-Of token exchange failed: {response.StatusCode} - {errorContent}");
        }
        
        var responseContent = await response.Content.ReadAsStringAsync();
        using var document = JsonDocument.Parse(responseContent);
        
        if (!document.RootElement.TryGetProperty("access_token", out var tokenElement))
        {
            throw new McpException("No access token in On-Behalf-Of response");
        }
        
        return tokenElement.GetString() ?? throw new McpException("Access token is null");
    }
}```


Hope that helps!

[eduardomb-aw]

@kimbell and @PederHP , I actually realized I had to fix an issue with the ClientOAuthProvider to make it compatible with Entra. I've create a bug for it (Bug 939), and a PR for it (PR940) with the fix and a couple of sample projects to demo it based on the existing ProtectedMcp sample.