Remove restrictive 30 character limit from username of AuthenticationForm.

[Chris Beaven]

While #8274 at least makes it possible to override the form now, the current default doesn't make sense.

The AuthenticationForm is not directly tied to the User model - any backend could use it. Therefore, there should not be a default max_length for the username.

[Russell Keith-Magee]

It may not be tied to the User model, but it is the natural authentication form *for* the User model.

[Chris Beaven]

It's the natural authentication form for *all* auth backends, the default of which uses the User model. Still think this is a rather silly constraint - if there was a max length check, it should happen in the backend.

[nehemiah jacob]

This 'wontfix' decision was taken nearly 6 years ago. Will there be a consideration to reopen this? Because I wish to use subclass AbstractUser model and impose email address as username. In this decade email addresses easily reach 30+ characters.

[Tim Graham]

The AuthenticationForm max_length was increased to 254 characters in bfcda7781a886ab2b7b41937c0f49c088f58a3d7 (Django 1.5) (#19130).