Improvements of the User model

[kurtisolo]

Terms

• [X] I have searched all open bug reports
• [X] I agree to follow activist's Code of Conduct

Behavior

User model in backend/authentication/models.py have some fields that should be discussed in my opinion.

Since the model is extending AbstractUser it is not recommended to have a user_name field, since there's already a default one. If I am not missing some specific reason for that I think we should then delete that field, or we'll have a useless double field. Same with the password field: Django already provides both the field and the security stuff (hashing, salting, etc.). Also I don't really like to have this field unnecessairly hardcoded for security reasons.

If there are some reasons for the choices that were already made maybe link me the relative discussion/documentation and sorry for the useless issue :P

[andrewtavis]

CC @to-sta for the discussion :)