ya se pueden registrar, faltaba username

authentication/models.py

@@ -9,7 +9,7 @@ class CustomUserManager(BaseUserManager):
         if not email:
             raise ValueError(_("El email es necesario"))
         email = self.normalize_email(email)
-        new_user = self.model(email=email, **extra_fields)
+        new_user = self.model(username=email, email=email, **extra_fields)
         new_user.set_password(password)
         new_user.save()
         return new_user