Session expiry?

Do the tokens in these demos expire? For example in flask-google-login/app.py I see that the user info is stored in the session: `session['user'] = token['userinfo']`, but I don't see any logic that has the webpage logout the user once the token expires. Through what means does authlib verify token validity?

Start with flask-google-login/app.py, especially the assignment to session['user'], then trace how the demo obtains and uses token['userinfo']. Document whether Authlib verifies token validity and how session state should behave after expiry; the issue is done when the expiry and logout behavior are clearly explained.

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