If you create a new Team Foundation Service project from http://tfs.visualstudio.com and specify “Git” as the underlying provider, I found that Xamarin and SourceTree on MacOS did NOT like the credentials. I would get a “not authorized” error.
To correct this, in your browser, while in your TFS project, click on your name in the top right and go to your profile:
Click the “Credentials” tab:
Click “Enable alternate credentials”:
Put in a password and use THAT password from alternate git clients. That’s it!