Azure Active Directory(AAD): Fixes stuck requests when background refresh fails to refresh token

[j82w]

Pull Request Template

Description

1. This bug can cause requests to get stuck because the semaphore was not getting released in the scenario where multiple requests are waiting for a new token. This only occurs in scenario where the background refresh has failed to get a new token.
2. This optimizes the scenario where multiple concurrent requests are waiting on the token. It will now return the original task that is getting the token. This prevents all the requests waiting in serial to get the failure. All the requests will return the same exception.

The existing test for this scenario use .Wait which blocked the threads which also blocked all the other task to simulate concurrent requests. The tasks now use a Task.Run to prevent them from getting blocked again and wait logic was converted to an async/await.

Type of change

Please delete options that are not relevant.

• [] Bug fix (non-breaking change which fixes an issue)
• [] New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [] This change requires a documentation update

Closing issues

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[FabianMeiswinkel]

LGTM - thank for the refactoring. I like the current synchronization mechanism.