Authentication between Android app and web service + facebook login

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http://stackoverflow.com – The only login option in my android application is login via Facebook. I would like to use Web service(asmx) and on each request, the server must validate that the user is authenticated via facebook. I found a solution: 1) Authenticate user to Facebook from Android application, 2) Get the FB auth token to the android app, 3) Forward the authentication token & facebook UID from Android to web server, 4) On web server, make Facebook API call with the submitted token. If the Facebook API call from web server returns valid authentication, and the user id is equal to the one su (HowTos)