How to properly define GAE's oauth2callback?

Question

The Using GAE / Decorators guide tells me that \"you need to add a specific URL handler to your application to handle the redirection from the authorization server back

Answer 1

This library does not ship in App Engine.

The version you should be using is google-api-python-client-1.1 hosted on the project download page.

I believe the version you're referring to is the (somewhat old) version of google-api-python-client included in the App Engine SDK. This is only included to perform simple OAuth 2.0 for appcfg.py and is a stable version for performing this simple task. Though it is in the SDK, it is NOT in the runtime and not endorsed as a current version of google-api-python-client for these reasons.

I'd also like to note that the article you linked explicitly points to installation instructions.

UPDATE: As noted there, your WSGI handler should contain the callback from the decorator

routes = [
    ('/update', UpdatePage),
    (decorator.callback_path, decorator.callback_handler()),
]
update = webapp2.WSGIApplication(routes, debug=True)

and your app.yaml should allow your main handler should either explicitly match the the route in decorator.callback_path

- url: /oauth2callback
  script: myapp.update

or should just route all remaining requests to your WSGI handler

- url: /.*
  script: myapp.update

(This second approach would likely warrant adding a 404 catch-all to the WSGI handler.)