Azure AD Multi Tenant ,.Net Core Web API with JWT Token

Question

So I raised this question Azure AD Multi Tenant ,.Net Core Web API with MSAL(Microsoft Authentication Libary) which showed me how to turn on the error output.

Why would I be getting this now with my token, at a guess is the aud right and the iss for a multi tenant ad token?

AuthenticationFailed: IDX10511: Signature validation failed. Keys tried: 'Microsoft.IdentityModel.Tokens.X509SecurityKey, KeyId: 'YMELHT0gvb0mxoSDoYfomjqfjYU', InternalId: '2c34a300-21bb-4eb1-b3b9-1944f1be7470'. , KeyId: YMELHT0gvb0mxoSDoYfomjqfjYU
'. 
kid: 'YMELHT0gvb0mxoSDoYfomjqfjYU'. 
Exceptions caught:
 ''.
token: '
{
    "alg": "RS256",
    "typ": "JWT",
    "nonce": "bWqlNum32nkLGFA4s5lE83AEZ6hRUzqi4r4-3JMZLdw",
    "x5t": "YMELHT0gvb0mxoSDoYfomjqfjYU",
    "kid": "YMELHT0gvb0mxoSDoYfomjqfjYU"
}
.{
    "aud": "00000003-0000-0000-c000-000000000000",
    "iss": "https://sts.windows.net/abc60396-1ed0-4fa3-a3d0-597adf1366a5/",
    "iat": 1584438416,
    "nbf": 1584438416,
    "exp": 1584442316,
    "acct": 0,
    "acr": "1",
    "aio": "42NgYNh7TvzDvOILBsl/7E+U+vxP6y5rmJERnny04o5ZM2vJjmwA",
    "amr": ["pwd"],
    "app_displayname": "AzureAdTest",
    "appid": "A134d6c8-8078-2924-9e90-98cef862eb9a",
    "appidacr": "0",
    "family_name": "Bob",
    "given_name": "Bob",
    "ipaddr": "111.111.124.18",
    "name": "Bob Powell",
    "oid": "5b2dfaea-41fb-4a76-93da-6b4c04041f4d",
    "platf": "3",
    "puid": "10032000A35A0EE1",
    "scp": "openid profile User.Read email",
    "sub": "NM4nVqUfyC-6pF66I1Wef8Bvl7rhnpB_UBv7fX-qMHU",
    "tid": "abc60396-1ed0-4fa3-a3d0-597adf1366a5",
    "unique_name": "[email protected]",
    "upn": "[email protected]",
    "uti": "-mwXtFoS1kGJjorQqzI0AA",
    "ver": "1.0",
    "xms_st": {
        "sub": "p7nf6_rRkoqINUHy3cl_qRQ2F-DaCfFwQgy6gTQv_QY"
    },
    "xms_tcdt": 1583932579
}
'.

My previous question was:

I believe I have the Microsoft Authentication Library (MSAL) JavaScript pulling back a JWT token, using azure AD multi tenant with the following config. Based of this link https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-convert-app-to-be-multi-tenant. I believe I only need the following two values.

clientId: "A134d6c8-8078-2924-9e90-98cef862eb9a" // this would be the app registrations client id(application)
authority: "https://login.microsoftonline.com/common"

How then can I configure a .net core 3 web api that can handle this JWT token and authenticate [Authorize] endpoints by me passing the Authorization: Bearer header.

I currently get this error in the response which is not very helpful!

AuthenticationFailed: IDX10511: Signature validation failed. Keys tried: '[PII is hidden. For more details, see https://aka.ms/IdentityModel/PII.]'. 
kid: '[PII is hidden. For more details, see https://aka.ms/IdentityModel/PII.]'. 
Exceptions caught:
 '[PII is hidden. For more details, see https://aka.ms/IdentityModel/PII.]'.
token: '[PII is hidden. For more details, see https://aka.ms/IdentityModel/PII.]'.

The Startup.cs code is as follows

using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.IdentityModel.Tokens;

namespace MultiTenantApi
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {

            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors(x =>
            {
                x.AddDefaultPolicy(cfg =>
                {
                    cfg.AllowAnyOrigin()
                        .AllowAnyHeader()
                        .AllowAnyMethod();
                });
            });

            services.AddAuthentication(cfg =>
                {
                    cfg.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                    cfg.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
                })
                .AddJwtBearer(opt =>
                {
                    opt.Authority = "https://login.microsoftonline.com/common";
                    opt.Audience = "api://A134d6c8-8078-2924-9e90-98cef862eb9a"; // Set this to the App ID URL for the web API, which you created when you registered the web API with Azure AD.
                    opt.TokenValidationParameters = new TokenValidationParameters
                    {
                        ValidateIssuer = false
                    };
                    opt.Events = new JwtBearerEvents()
                    {
                        OnAuthenticationFailed = AuthenticationFailed
                    };
                });

            services.AddControllers();

        }

        private Task AuthenticationFailed(AuthenticationFailedContext arg)
        {
            // For debugging purposes only!
            var s = $"AuthenticationFailed: {arg.Exception.Message}";
            arg.Response.ContentLength = s.Length;
            arg.Response.Body.WriteAsync(Encoding.UTF8.GetBytes(s), 0, s.Length);
            return Task.FromResult(0);
        }
        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            app.UseStaticFiles(); // Added

            app.UseRouting();
            app.UseCors(); //Added

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

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });

        }

    }
}

Answer 1

With the help of juunas response above, I change my scope from user.read to the following this is my client id(application id) followed by .default

var tokenRequest = {
    scopes: ["A134d6c8-8078-2924-9e90-98cef862eb9a/.default"]
};
await this.app.acquireTokenSilent(tokenRequest)
   ... etc

After this I could see aud value was no longer the graph api one

"aud": "A134d6c8-8078-2924-9e90-98cef862eb9"

In the C# API my code now works with this in the ConfigureServices Startup.cs file

services.AddAuthentication(cfg =>
{
    cfg.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
    cfg.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
})
.AddJwtBearer(opt =>
{
    opt.Authority = "https://login.microsoftonline.com/common";
    opt.Audience = "api://A134d6c8-8078-2924-9e90-98cef862eb9a"; // Set this to the App ID URL for the web API, which you created when you registered the web API with Azure AD.

    opt.TokenValidationParameters = new TokenValidationParameters
    {
        ValidateIssuer = true, 
        ValidateAudience = true, 
        ValidAudiences = new List<String>
        {
            // you could add a list of valid audiences
            "A134d6c8-8078-2924-9e90-98cef862eb9a"
        }, 
        ValidIssuers = new List<string>
        {
            // Add tenant id after https://sts.windows.net/
            "https://sts.windows.net/{YourTenantId}"
        }
    };
    opt.Events = new JwtBearerEvents()
    {
        OnAuthenticationFailed = AuthenticationFailed
    };
});