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Why does the MS Teams login not work?



Why is the MS Teams login not working?


By default, the Connect Client attempts to connect to MS Teams using the default proxy. If this connection attempt fails, you will find an error message in the Connect Client log like the following:

AuthenticateAsync: TeamsConnection - Exception in AcquireTokenByIntegratedWindowsAuth Exception: System.Net.Http.HttpRequestException: Error sending request. ---> System.Net.WebException: The remote server returned an error: (407) Proxy authentication required.

In the Connect Client itself, the behavior manifests itself with the following message:



To suppress this behavior, you need to manipulate the registry. Search for "regedit" in Windows search and open Registry Editor.

Then navigate to the path HKEY_CURRENT_USER\Software\C4B.

Here you must now create a folder named "xp4teams" and the key "enableproxy" of type string with the value 0:


Explanation of the possible values:

  • 0 = no proxy
  • 1 = use default proxy
  • folder or entry "enableproxy" is missing = use default proxy

Then restart the Connect Client and test the behavior.


If access is to be enabled in the proxy, enable the following URLs in the proxy for Teams matching:


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