Allow mapping payload username field to actual

[willdady]

I have a custom User model where USERNAME_FIELD = 'email' however I'd like to be able to submit login credentials as:

{
  username: 'foo@example.com',
  password: 'mypassword'
}

Not

{
  email: 'foo@example.com',
  password: 'mypassword'
}

I'm wanting to make the request compliant with OAuth2 Access Token Request.

Currently this is not possible as JSONWebTokenSerializer creates it's username field by inspecting UserModel.USERNAME_FIELD. Having a setting for mapping payload username to model username would be useful.

[avral]

Same problem :(