Call to DeviceCodeCredential.GetTokenAsync() never returns - microsoft-graph-api

Question

To be able to call Microsoft.Graph API on my .Net MAUI app, I need to get an access token. I followed this documentation:
https://learn.microsoft.com/en-us/graph/tutorials/dotnet?tabs=aad&tutorial-step=3
And here is my code:
internal class GraphHelper
{
private static string[] _graphUserScopes = new[] { "https://graph.microsoft.com/.default" };
// User auth token credential
private static DeviceCodeCredential? _deviceCodeCredential;
// Client configured with user authentication
private static GraphServiceClient? _userClient;
public static void InitializeGraphForUserAuth(Func<DeviceCodeInfo, CancellationToken, Task> deviceCodePrompt)
{
string adTenantId = "MY TENANT ID";
string adClientId = "MY CLIENT ID";
_deviceCodeCredential = new DeviceCodeCredential(deviceCodePrompt,
adTenantId, adClientId);
_userClient = new GraphServiceClient(_deviceCodeCredential, _graphUserScopes);
}
public static async Task<string> GetUserTokenAsync()
{
// Ensure credential isn't null
_ = _deviceCodeCredential ??
throw new NullReferenceException("Graph has not been initialized for user auth");
// Ensure scopes isn't null
_ = _graphUserScopes ?? throw new ArgumentNullException("Argument 'scopes' cannot be null");
// Request token with given scopes
TokenRequestContext context = new TokenRequestContext(_graphUserScopes);
AccessToken response = default;
try
{
response = await _deviceCodeCredential.GetTokenAsync(context);
}
catch (Exception ex)
{
}
return response.Token;
}
}
Call to await _deviceCodeCredential.GetTokenAsync(context) never comes back. And only in about 10 minutes the following exception is thrown:
Azure.Identity.AuthenticationFailedException: DeviceCodeCredential authentication failed: Verification code expired before contacting the server
I would like to know how I can diagnose and/or fix this problem.

Answer 1

Call to await ... never comes back.
await that never returns is a deadlock.
To find out where the problem starts, and fix it:
Put a breakpoint at start of GetUserTokenAsync.
Look at call stack. Check each method in call stack to see if it is declared async (you'll have to go to source code of each method).
What is the first method you encounter that is NOT declared async?
Look at the async method it calls: is there an await in front of that call? If not, that is your problem.
Starting a chain of async/await calls from a non-async context can cause a thread deadlock.
Typically happens on UI thread. Most common mistake is attempting to call inside a constructor.
IF it is the problem I describe, try adding await.
Build. If no compile error, it should now work.
If there is compile error at that await, a fix is to create an async context to do the await in.
To await on UI thread (MainThread):
// An alternative is "MainThread.BeginInvokeOnMainThread".
Dispatcher.Dispatch(async () =>
{
... = await ...;
// Code after your await line goes here.
}
// DO NOT have any code here, unless it is okay to run it BEFORE the dispatched await finishes.
To await on a background thread:
Task.Run(async () =>
... same logic as above ...