UseJwtBearerAuthentication failed: Unauthorized to

Question

I am having a web api service and a web client application to access the web api. Both are registered on azure active directory. However, when the web client application tried to access web api, I got :

ReasonPhrase: 'Unauthorized'
WWW-Authenticate: Bearer error=\"invalid_token\", error_description=\"The signature is invalid

Then I checked the token on https://jwt.io/, it indeed showed "invalid signature". However, I have no idea what is wrong here.

Here is how I retrieved the token:

string authority = "https://login.windows.net/tenantid-log-number/oauth2/token";
string clientID = "83adf895-681a-4dd6-9dfb-2a1484dd4188";

string resourceUri = "https://tenant.onmicrosoft.com/webapiservice";
string appKey = "anJxg3N/5dqiHKx+4zwzFB9A6dN5HdqSitdSOpxzVd="; 

ClientCredential clientCredential = new ClientCredential(clientID, appKey);

AuthenticationContext ac = new AuthenticationContext(authority);
Task<AuthenticationResult> authResult = ac.AcquireTokenAsync(resourceUri, clientCredential);
return authResult.Result.AccessToken;

Here is how I access web api service:

HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://webapiservice.azurewebsites.net/");
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);

HttpResponseMessage response = client.GetAsync("api/values").Result;

Here is how web api service validates the access:

app.UseJwtBearerAuthentication(new JwtBearerOptions
{
     AutomaticAuthenticate = true,
     AutomaticChallenge = true,

     TokenValidationParameters = new TokenValidationParameters
     {
          ValidateAudience = true,
          ValidAudience = "https://tenant.onmicrosoft.com/webapiservice",
      }
  });

Anything wrong here?

Thanks

Answer 1

Based on your configuration and code snippets, it look like you're trying to setup a Web API for .Net Core using the Azure AD v1 endpoint.

For .Net Core using the Azure AD v1 endpoint, you should use UseJwtBearerAuthentication as follows:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    // ...
    // Other stuff
    // ...

    app.UseJwtBearerAuthentication(
        new JwtBearerOptions
        {
            Authority = string.Format("https://login.microsoftonline.com/{0}/", 
                Tenant),
            Audience = ClientId
        });
}

---

For reference, here are some other setups that can be used:

For .Net using the Azure AD v1 endpoint, you should use UseWindowsAzureActiveDirectoryBearerAuthentication

Here's a snippet from the official .NET Web API sample, sample that showcases how to set this up:

public void ConfigureAuth(IAppBuilder app)
{
    app.UseWindowsAzureActiveDirectoryBearerAuthentication(
        new WindowsAzureActiveDirectoryBearerAuthenticationOptions
        {
            Audience = ClientId,
            Tenant = Tenant
        });
}

For .Net using the Azure AD v2 endpoint, you should use UseOAuthBearerAuthentication as follows:

public void ConfigureAuth(IAppBuilder app)
{
    TokenValidationParameters tvps = new TokenValidationParameters
    {
        // Accept only those tokens where the audience of the token is equal to the client ID of this app
        ValidAudience = ClientId
    };

    app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions
    {
        // This SecurityTokenProvider fetches the Azure AD B2C metadata & signing keys from the OpenIDConnect metadata endpoint
        AccessTokenFormat = new JwtFormat(tvps, new OpenIdConnectCachingSecurityTokenProvider(String.Format("https://login.microsoftonline.com/{0}", Tenant)))
    });
}

For .Net Core using the Azure AD v2 endpoint, you should use UseJwtBearerAuthentication as follows:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    // ...
    // Other stuff
    // ...

    app.UseJwtBearerAuthentication(
        new JwtBearerOptions
        {
            Authority = string.Format("https://login.microsoftonline.com/{0}/v2.0/", 
                Tenant),
            Audience = ClientId
        });
}