If you can use python decorator in your app engine project, there is tiny and smart example below which you can use it:
The print will be user email
def uzman(func):
def check_auth(*args, **kwargs):
user=users.get_current_user()
print user
return func(*args, **kwargs)
return check_auth
class TestModule(webapp.RequestHandler):
@uzman
def get(self):
pass