login.py

from django.contrib.auth.forms import AuthenticationForm
from django.forms import ValidationError

class CustomLoginForm(AuthenticationForm):

    #overriding clean method to change default authentication behaviour
    def clean(self):
        userid = self.cleaned_data.get('username')
        password = self.cleaned_data.get('password')
        
        if userid and password:
            #the backends will be picked from the settings from the variable named AUTHENTICATION_BACKENDS
            #and the authentication method of each of one will be called in the same order as the order in the AUTHENTICATION_BACKENDS list
            self.user_cache = authenticate(
                userid=userid, 
                password=password
            )

            if self.user_cache is None:
                raise forms.ValidationError(
                    self.error_messages['invalid_login'],
                    code='invalid_login',
                    params={'username': self.username_field.verbose_name},
                )
            else:
                self.confirm_login_allowed(self.user_cache)
        
        return self.cleaned_data

from django.forms import ValidationError
line 20 raise forms.ValidationError(
You don't need the word forms