Inconsistency in Documentation between Custom Authentication Backends and Custom Users

[Alex Rothberg]

The docs for writing an authentication backend state:

The get_user method takes a user_id – which could be a username, database ID or whatever, but has to be the primary key of your User object – and returns a User object.

whereas the docs for writing a custom user state:

Django expects your custom User model to meet some minimum requirements.
Your model must have an integer primary key.

I would expect that username need not be an integer but that seems to be disallowed by the user model spec.

[Tim Graham]

Duplicate of #24429