Custom User Model extending AbstractUser, authenticate return None
SOLVED!
The problem was not to extend AbstracUser, the problem was when i saved the user,
CustomUser(username='myusername', password='mypassword'), the password is saved like plain text and de function authenticate() doesn't work with this.
It's necessary save user usinng UserCreationForm, or extending it, the most important is save() method because use set_password() method which set encrypted password so authenticate() method works.
I want create my custom user extending AbstractUser, but when i want authenticate my custom user return None.
When i create CustomUser() is stored in database but the passwowrd is not encrypted. Can i use authenticate function of banckend default? or i must create a custom backend for my custom user. 
i added:
AUTH_USER_MODEL = 'mysite.customuser' 
I think extending of AbstractUser, my class don't have same method or something is wrong