suport login via oauth token to avoid having to login twice

[Michael Vogt]

To avoid having to login via the webui for a purchase we should support (re)using the oauth token that we obtained
from ubuntu sso login. The workflow needs to change slightly then.

For a purchase:
1. hit https://software-center.ubuntu.com/login_by_token/ and sign that request with a oauth signature
2. wait until that view returns "login succeeded" (views.py:335: return http.HttpResponse('login succeeded'))
3. then go and load the usual "purchase url" as usual

Alternatively (not there yet) once the server is ready:
1. hit ttps://software-center.ubuntu.com/login_by_token/?next=/subscription/+new" ..

[Michael Vogt (mvo)]

To test the oauth code from the branch lp:~mvo/software-center/oauth-from-webkit:

$ PYTHONPATH=. python softwarecenter/ui/gtk3/views/purchaseview.py https://software-center.ubuntu.com/api/2.0/subscriptions

[Michael Vogt (mvo)]

<achuni> there is one problem, of course
 this will log you into sca.
 but, unless we log you into sso, when you try to log into Pay you'll be prompted to log in again

So from the comment from achuni this needs a bit more server side work.