Enforcing password strength requirements with django.contrib.auth.views.password_change

We have a Django application that requires a specific level of password complexity. We currently enforce this via client-side JavaScript which can easily be defeated by someone who is appropriately motivated.

I cannot seem to find any specific information about setting up server-side password strength validation using the django contrib built in views. Before I go about re-inventing the wheel, is there a proper way to handle this requirement?

I also went with a custom form for this. In urls.py specify your custom form:

(r'^change_password/$', 'django.contrib.auth.views.password_change',
     {'password_change_form': ValidatingPasswordChangeForm}),

Inherit from PasswordChangeForm and implement validation:

from django import forms
from django.contrib import auth

class ValidatingPasswordChangeForm(auth.forms.PasswordChangeForm):
    MIN_LENGTH = 8

    def clean_new_password1(self):
        password1 = self.cleaned_data.get('new_password1')

        # At least MIN_LENGTH long
        if len(password1) < self.MIN_LENGTH:
            raise forms.ValidationError("The new password must be at least %d characters long." % self.MIN_LENGTH)

        # At least one letter and one non-letter
        first_isalpha = password1[0].isalpha()
        if all(c.isalpha() == first_isalpha for c in password1):
            raise forms.ValidationError("The new password must contain at least one letter and at least one digit or" \
                                        " punctuation character.")

        # ... any other validation you want ...

        return password1

Django 1.9 offers a built-in password validation to help prevent the usage of weak passwords by users. It's enabled by modifing the AUTH_PASSWORD_VALIDATORS setting in our project. By default Django comes with following validators:

• UserAttributeSimilarityValidator, which checks the similarity between the password and a set of attributes of the user.
• MinimumLengthValidator, which simply checks whether the password meets a minimum length. This validator is configured with a custom option: it now requires the minimum length to be nine characters, instead of the default eight.
• CommonPasswordValidator, which checks whether the password occurs in a list of common passwords. By default, it compares to an included list of 1000 common passwords.
• NumericPasswordValidator, which checks whether the password isn’t entirely numeric.

This example enables all four included validators:

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
        'OPTIONS': {
            'min_length': 9,
        }
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]

As some eluded to with the custom validators, here's the approach I would take...

Create a validator:

from django.core.exceptions import ValidationError
from django.utils.translation import ugettext as _

def validate_password_strength(value):
    """Validates that a password is as least 7 characters long and has at least
    1 digit and 1 letter.
    """
    min_length = 7

    if len(value) < min_length:
        raise ValidationError(_('Password must be at least {0} characters '
                                'long.').format(min_length))

    # check for digit
    if not any(char.isdigit() for char in value):
        raise ValidationError(_('Password must contain at least 1 digit.'))

    # check for letter
    if not any(char.isalpha() for char in value):
        raise ValidationError(_('Password must contain at least 1 letter.'))

Then add the validator to the form field you're looking to validate:

from django.contrib.auth.forms import SetPasswordForm

class MySetPasswordForm(SetPasswordForm):

    def __init__(self, *args, **kwargs):
        super(MySetPasswordForm, self).__init__(*args, **kwargs)
        self.fields['new_password1'].validators.append(validate_password_strength)