WIP: Authorization Support (Using ASP.NET Core Native AuthN/AuthZ Integration)

[localden]

Implements the authorization flow for clients and servers, per specification. Instead of re-implementing everything from scratch, this follows the suggestions from #349 and uses the native ASP.NET Core constructs to handle post-discovery steps server-side.

Developer experience

Server

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

var builder = WebApplication.CreateBuilder(args);

var serverUrl = "http://localhost:7071/";
var tenantId = "a2213e1c-e51e-4304-9a0d-effe57f31655";
var instance = "https://login.microsoftonline.com/";

builder.Services.AddAuthentication(options =>
{
    options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
    options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
})
.AddJwtBearer(options =>
{
    options.Authority = $"{instance}{tenantId}/v2.0";
    options.TokenValidationParameters = new TokenValidationParameters
    {
        ValidateIssuer = true,
        ValidateAudience = true,
        ValidateLifetime = true,
        ValidateIssuerSigningKey = true,
        ValidAudience = "167b4284-3f92-4436-92ed-38b38f83ae08",
        ValidIssuer = $"{instance}{tenantId}/v2.0",
        NameClaimType = "name",
        RoleClaimType = "roles"
    };

    options.MetadataAddress = $"{instance}{tenantId}/v2.0/.well-known/openid-configuration";

    options.Events = new JwtBearerEvents
    {
        OnTokenValidated = context =>
        {
            var name = context.Principal?.Identity?.Name ?? "unknown";
            var email = context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
            Console.WriteLine($"Token validated for: {name} ({email})");
            return Task.CompletedTask;
        },
        OnAuthenticationFailed = context =>
        {
            Console.WriteLine($"Authentication failed: {context.Exception.Message}");
            return Task.CompletedTask;
        },
        OnChallenge = context =>
        {
            Console.WriteLine($"Challenging client to authenticate with Entra ID");
            return Task.CompletedTask;
        }
    };
})
.AddMcp(options =>
{
    options.ResourceMetadataProvider = context => 
    {
        var metadata = new ProtectedResourceMetadata
        {
            BearerMethodsSupported = { "header" },
            ResourceDocumentation = new Uri("https://docs.example.com/api/weather"),
            AuthorizationServers = { new Uri($"{instance}{tenantId}/v2.0") }
        };

        metadata.ScopesSupported.AddRange(new[] {
            "api://167b4284-3f92-4436-92ed-38b38f83ae08/weather.read" 
        });
        
        return metadata;
    };
});

builder.Services.AddAuthorization();

builder.Services.AddHttpContextAccessor();
builder.Services.AddMcpServer()
.WithTools<WeatherTools>()
.WithHttpTransport();

builder.Services.AddSingleton(_ =>
{
    var client = new HttpClient() { BaseAddress = new Uri("https://api.weather.gov") };
    client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("weather-tool", "1.0"));
    return client;
});

var app = builder.Build();

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

// Use the default MCP policy name that we've configured
app.MapMcp().RequireAuthorization();

Console.WriteLine($"Starting MCP server with authorization at {serverUrl}");
Console.WriteLine($"PRM Document URL: {serverUrl}.well-known/oauth-protected-resource");
Console.WriteLine("Press Ctrl+C to stop the server");

app.Run(serverUrl);

HTTP context in tools

.AddHttpContextAccessor is used to ensure that tools can access the HTTP context (such as the authorization header contents).

Tools that want to use the HTTP context will need to amend their signatures to include a reference to IHttpContextAccessor, like this:

[McpServerTool, Description("Get weather alerts for a US state.")]
public static async Task<string> GetAlerts(
    HttpClient client,
    IHttpContextAccessor httpContextAccessor,
    [Description("The US state to get alerts for. Use the 2 letter abbreviation for the state (e.g. NY).")] string state)

Client

using ModelContextProtocol.Client;
using ModelContextProtocol.Protocol.Transport;

namespace ProtectedMCPClient;

class Program
{
    static async Task Main(string[] args)
    {
        Console.WriteLine("Protected MCP Weather Server");
        Console.WriteLine();

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

        var tokenProvider = new BasicOAuthAuthorizationProvider(
            new Uri(serverUrl), 
            clientId: "6ad97b5f-7a7b-413f-8603-7a3517d4adb8",
            redirectUri: new Uri("http://localhost:1179/callback"),
            scopes: ["api://167b4284-3f92-4436-92ed-38b38f83ae08/weather.read"]
        );

        Console.WriteLine();
        Console.WriteLine($"Connecting to weather server at {serverUrl}...");

        try
        {
            var transportOptions = new SseClientTransportOptions
            {
                Endpoint = new Uri(serverUrl),
                Name = "Secure Weather Client"
            };

            var transport = new SseClientTransport(transportOptions, tokenProvider);
            var client = await McpClientFactory.CreateAsync(transport);

            var tools = await client.ListToolsAsync();
            if (tools.Count == 0)
            {
                Console.WriteLine("No tools available on the server.");
                return;
            }

            Console.WriteLine($"Found {tools.Count} tools on the server.");
            Console.WriteLine();

            if (tools.Any(t => t.Name == "GetAlerts"))
            {
                Console.WriteLine("Calling GetAlerts tool...");

                var result = await client.CallToolAsync(
                    "GetAlerts",
                    new Dictionary<string, object?> { { "state", "WA" } }
                );

                Console.WriteLine("Result: " + result.Content[0].Text);
                Console.WriteLine();
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
            if (ex.InnerException != null)
            {
                Console.WriteLine($"Inner error: {ex.InnerException.Message}");
            }

            #if DEBUG
            Console.WriteLine($"Stack trace: {ex.StackTrace}");
            #endif
        }

        Console.WriteLine("Press any key to exit...");
        Console.ReadKey();
    }
}

[tolginator]

I was expecting to see the Name="get_alerts" annotation. Would the Name property be auto-deduced from the function name?

[tolginator]

Re: AuthZ checks.
I was expecting to see something like the following at the class definition or on a per-method basis like the usual ASP.Net role annotations.

    [Authorize(Policy = "AuthenticatedUserPolicy")]
    [RequiredScope("Weather")]
    public class WeatherTools

How would I specify required roles (or mor egenerally, AuthZ requirements) on a per-class/method basis?

[tolginator]

nit: Isn't this the same as https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/httpclient-extensions?

[tolginator]

nit: Does it need/have to be sealed?

[darrelmiller]

Using ReadAsStream and then Deserializing the stream will save allocating the string because the Stream contents are not buffered.

[darrelmiller]

Same as above. Use ReadAsStream

[stephentoub]

Does this need to be public? Who consumes this? Are these documented in the MCP spec?