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Do you want to use FaceBook, other accounts to sign in your application, then you remember the Access token for next time? If so, you can use
Xamarin.Auth to achieve it
For FaceBook account auth, you can Google search(Due to the policy, I cannot give you link directly): Social Media Authentication – Facebook login in Xamarin Forms
For Google account auth, you can Google search: Authenticate users through Google with Xamarin.Auth
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