Remove support for OpenID

[François Marier]

The Django OpenID auth plugin we rely on has been removed from Debian:

  https://tracker.debian.org/news/741799/django-openid-auth-removed-from-testing/

since it's incompatible with Django 1.9:

  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=806352

Unless there is a replacement plugin, our only option is to remove support for OpenID logins and the ability to associate photos with OpenIDs. This will require updating the API documentation: https://wiki.libravatar.org/api/

This would obsolete bug 1159583, bug 1186727, bug 769782 and bug 1041050. It would also unblock supporting MySQL (bug 1018682).

[François Marier (fmarier)]

Here are the awstats for the different endpoints (March 2018):

                        Viewed Size Entry Exit
/account/login/ 1,101 5.49 KB 315 248
/openid/login/ 216 2.89 KB 42 34
/account/add_email/ 205 2.50 KB 5
/account/add_openid/ 53 2.52 KB 4

Note that you have to hit /account/login before clicking on /openid/login, but it gives an idea about how many users actually use OpenID logins.

Here is adding an email address v. adding an OpenID:

                        Viewed Size Entry Exit
/account/add_email/ 205 2.50 KB 5
/account/add_openid/ 53 2.52 KB 4

In terms of user accounts, here are the stats for 2018-05-19:

User accounts with:
- at least one confirmed email: 3531
- at least confirmed OpenID: 2119
- a confirmed OpenID and no email: 1386

In order words, dropping OpenID will prevent 1386 users from being able to login. That said, they won't need to login anymore since Libravatar won't support associating/serving photos for OpenIDs anymore.