I have a web application hosted in Google app engine and i need to handle some APIs (calendar). I need to authenticate the user via OAuth and to call an API.
2 Answers
I'm going to guess you are talking about the Google Calendar API, since you didn't specify. Information about using the Google Calendar API (in Java) is here. The document isn't specifically tailored to App Engine, but you can see some App Engine examples in the client library distribution.
Comments
You can try scribe-java. It works on GAE. Or maybe scribe-up which is an extension to it and supports getting user profiles out of the box.