get_login_url goes to blank page when coming from naked url
When accessing the site via "example.com", self.request.uri is from that domain, which is the domain where the cookie is created. When it then redirects back, it goes to "www.example.com", which has no cookie, but your site is expecting a user to be logged in.
Suggestions: use a relative path like / (or webapp2's uri routing) instead of a full URI, or first redirect to www.example.com before doing the login.
I just started hosting my app on a new domain. I selected a url forwarding option with my registrar. Which seems to work. example.com didn't work before (as opposed to the subdomain www.example.com) but now it does. 
The problem is that if I access the site via example.com and try to login, users.create_login_url(self.request.uri), I go to a blank page. If I go to www.example.com the login works fine. In both cases self.request.uri is returning the www subdomain, even though in the first case example.com is still shown in the browser.
I don't really know much about this stuff. Any tips on where I should go from here?