c# - Unable to get bearer token from Azure AD to use with API App

Question

I have an MVC application that needs to access private API App in Azure that is protected with Azure AD authentication. So I need to get Azure AD bearer token, transfer it into Zumo-Auth token and use it to access the API App.

I'm going through this tutorial and everything is working fine until the point when I need to request the token from authContext. Here is the snippet of a code:

var authContext = new AuthenticationContext(
    "https://login.microsoftonline.com/MyADDomain.onmicrosoft.com");

ClientCredential credential = new ClientCredential(
    "04472E33-2638-FAKE-GUID-F826AF4928DB", 
    "OMYAPIKEY1x3BLAHEMMEHEHEHEHEeYSOMETHINGRc=");

// Get the AAD token.
var appIdUri = 
    "https://MyAppGateway-814485545465FAKE4d5a4532cd.azurewebsites.net/login/aad";

//var appIdUri = "https://MyADDomain.onmicrosoft.com/MyAppName";
//var appIdUri = "https://MyADDomain.onmicrosoft.com/";
//var appIdUri = "https://graph.windows.net";

AuthenticationResult result = 
    authContext.AcquireToken(appIdUri, credential); // <-- can't get the token from AD

// downhill from here
var aadToken = new JObject();
aadToken["access_token"] = result.AccessToken;
var appServiceClient = new AppServiceClient(
    "https://MyAppGateway-814485545465FAKE4d5a4532cd.azurewebsites.net/");

// Send the AAD token to the gateway and get a Zumo token
var appServiceUser = await appServiceClient.LoginAsync("aad", aadToken);

The line with authContext.AcquireToken(appIdUri, credential) is the one causing trouble.

If as appIdUri I give https://MyAppGateway-814485545465FAKE4d5a4532cd.azurewebsites.net/login/aad, I get exception:

400: AdalServiceException: AADSTS50001: Resource 'https://MyAppGateway-814485545465FAKE4d5a4532cd.azurewebsites.net/login/aad' is not registered for the account.

But this exact line is in the list of Reply Url in the AD Application

When I try to use https://MyADDomain.onmicrosoft.com/MyAppName or https://MyADDomain.onmicrosoft.com/ as appIdUri I get a different exception message:

400: AdalServiceException: AADSTS50105: Application '04472E33-2638-FAKE-GUID-F826AF4928DB' is not assigned to a role for the application 'https://MyADDomain.onmicrosoft.com/MyAppName'

Or

400: AdalServiceException: AADSTS50105: Application '04472E33-2638-FAKE-GUID-F826AF4928DB' is not assigned to a role for the application 'https://MyADDomain.onmicrosoft.com/'

In both cases I had the App ID URI in the AD Application set to 'https://MyADDomain.onmicrosoft.com/MyAppName' or 'https://MyADDomain.onmicrosoft.com/'. And both of the names in the list of Reply URL.

Eventually after enough tries I have put https://graph.windows.net as appIdUri and got the bearer token back. But the token was given with expiry date in the past (about 1 minute in the past). So I could not do anything further with this. And got 401-Unauthenticated when tried to use the token to login into API App.

What am I missing?

Answer 1

I have gone ahead and followed the tutorial to which you referred: Call an Azure API app from a web app client authenticated by Azure Active Directory

1. Create an Azure API Api that returns contact data
2. Deploy the API App to Azure App Service.
3. Secure the API App using Azure Active Directory.

Then I was able to retrieve the token, and as you can see from the following demo, my code is no different than your code, except that it using a later version of the using Microsoft.IdentityModel.Clients.ActiveDirectory libraries that use Async.

Get access token from AAD

class Program
{
    static void Main(string[] args)
    {
        var authContext = new AuthenticationContext(Constants.AUTHORITY);
        var credential = 
            new ClientCredential(Constants.CLIENT_ID, Constants.CLIENT_SECRET);
        var result = (AuthenticationResult)authContext
            .AcquireTokenAsync(Constants.API_ID_URL, credential)
            .Result;
        var token = result.AccessToken;
        Console.WriteLine(token.ToString());
        Console.ReadLine();
    }
}

Constants

AUTHORITY. The first segment of this is https://login.microsoftonline.com. The final segment is an allowed tenant. We set the allowed tenant at portal.azure.com, going to the Gateway for our application, and choosing Settings > Identity > Azure Active Directory > Allowed Tenants. My tenant is bigfontoutlook.onmicrosoft.com.

CLIENT_ID. We retrieve this client id from the application that we added to Azure Active Directory. Find this at manage.windowsazure.com > Active Directory > Your Directory > APPLICATIONS > Your Application > CONFIGURE. Once we have retrieved it, we must add it to our Gateway's Azure Active Directory settings in the Client ID field.

CLIENT_SECRET. We create/retrieve this in the same location that we retrieve our client id.

API_ID_URL. We retrieve this within the Gateway blade for our Web API App by choosing Settings > Identity > Azure Active Directory > App URL.

Here are the ones that work for me.

class Constants
{
    public const string AUTHORITY =
     "https://login.microsoftonline.com/bigfontoutlook.onmicrosoft.com/";

    public const string CLIENT_ID = 
      "0d7dce06-c3e3-441f-89a7-f828e210ff6d";

    public const string CLIENT_SECRET =
      "AtRMr+Rijrgod4b9Q34i/UILldyJ2VO6n2jswkcVNDs=";

    public const string API_ID_URL = 
      "https://mvp201514929cfaaf694.azurewebsites.net/login/aad";
}

Final decoded JWT

This is what the decoded JWT access token contains.

{
 typ: "JWT",
 alg: "RS256",
 x5t: "MnC_VZcATfM5pOYiJHMba9goEKY",
 kid: "MnC_VZcATfM5pOYiJHMba9goEKY"
}.
{
 aud: "https://mvp201514929cfc350148cfa5c9b24a7daaf694.azurewebsites.net/login/aad",
 iss: "https://sts.windows.net/0252f597-5d7e-4722-bafa-0b26f37dc14f/",
 iat: 1442346927,
 nbf: 1442346927,
 exp: 1442350827,
 ver: "1.0",
 tid: "0252f597-5d7e-4722-bafa-0b26f37dc14f",
 oid: "5a6f33eb-b622-4996-8a6a-600dce355389",
 sub: "5a6f33eb-b622-4996-8a6a-600dce355389",
 idp: "https://sts.windows.net/0252f597-5d7e-4722-bafa-0b26f37dc14f/",
 appid: "0d7dce06-c3e3-441f-89a7-f828e210ff6d",
 appidacr: "1"
}.

Note: It's a throwaway app in a throwaway active directory account with a throwaway resource group, so showing my security credentials is a non-issue.

Diagram just to be sure :)