Hello Sven,
your question is more related to Xamarin, OAuth, web service and so on, you could repost a new thread to related forum for a certain question.
Xamarin forum,
Asp.Net forum, Oauth forum.
The Visual C# discuss and ask the C# programming language, IDE, libraries, samples and tools. If you have some grammar or code errors, please feel free to contact us. We will try our best to give you a solution.
Best Regards,
Neil Hu
MSDN Community Support
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