The page dedicated to problems of implementing OAuth2 as a reusable, extendable and maintainable library rfc6749.
problem no.1 : still no clear picture of OAuth2
<place your image here>
problem no.2 : inherent complexity
a list of challenges to approach when implementing OAuth2 library:
<insert your problems here>
problem no.3 : no problem visibility
<merge and update information from http://pydanny.com/the-sorry-state-of-python-oauth-providers.html>
references
https://developers.google.com/api-client-library/python/guide/aaa_oauth
https://github.com/hiidef/oauth2app - Django, MIT
https://pypi.python.org/pypi/rauth - client (consumer) side, MIT, PyPI uses it