# Custom Behavior

There are times that the default `LDAPBackend` behavior may be insufficient for your needs. In those cases, you can further customize the behavior by following these general steps:

- Create your own `LDAPBackend` subclass.

- Use `default_settings` to define any custom settings you may want to use.

- Override `authenticate_ldap_user()` hook and/or any other method as needed.

- Define additional methods and attributes as needed.

- Access your custom settings via `self.settings` inside your `LDAPBackend` subclass.

## Subclassing LDAPBackend

You can implement your own `LDAPBackend` subclass if you need some custom behavior. For example, you want to only allow 50 login attempts every 30 minutes, and those numbers may change as needed. Furthermore, any successful login attempt against the LDAP server must send out an SMS notification, but there should be an option to limit this behavior to a specific set of usernames based on a regex. One can accomplish that by doing something like this:

    # mypackage.ldap

    import re

    from django.core.cache import cache

    from django_auth_ldap.backend import LDAPBackend

    class CustomLDAPBackend(LDAPBackend):
        default_settings = {
            "LOGIN_COUNTER_KEY": "CUSTOM_LDAP_LOGIN_ATTEMPT_COUNT",
            "LOGIN_ATTEMPT_LIMIT": 50,
            "RESET_TIME": 30 * 60,
            "USERNAME_REGEX": r"^.*$",
        }

        def authenticate_ldap_user(self, ldap_user, password):
            if self.exceeded_login_attempt_limit():
                # Or you can raise a 403 if you do not want
                # to continue checking other auth backends
                print("Login attempts exceeded.")
                return None
            self.increment_login_attempt_count()
            user = ldap_user.authenticate(password)
            if user and self.username_matches_regex(user.username):
                self.send_sms(user.username)
            return user

        @property
        def login_attempt_count(self):
            return cache.get_or_set(
                self.settings.LOGIN_COUNTER_KEY, 0, self.settings.RESET_TIME
            )

        def increment_login_attempt_count(self):
            try:
                cache.incr(self.settings.LOGIN_COUNTER_KEY)
            except ValueError:
                cache.set(self.settings.LOGIN_COUNTER_KEY, 1, self.settings.RESET_TIME)

        def exceeded_login_attempt_limit(self):
            return self.login_attempt_count >= self.settings.LOGIN_ATTEMPT_LIMIT

        def username_matches_regex(self, username):
            return re.match(self.settings.USERNAME_REGEX, username)

        def send_sms(self, username):
            # Implement your SMS logic here
            print("SMS sent!")

    # settings.py

    AUTHENTICATION_BACKENDS = [
        # ...
        "mypackage.ldap.CustomLDAPBackend",
        # ...
    ]

## Using default_settings

While you can use your own custom Django settings to create something similar to the sample code above, there are a couple of advantages in using `default_settings` instead.

Following the sample code above, one advantage is that the subclass will now automatically check your Django settings for `AUTH_LDAP_LOGIN_COUNTER_KEY`, `AUTH_LDAP_LOGIN_ATTEMPT_LIMIT`, `AUTH_LDAP_RESET_TIME`, and `AUTH_LDAP_USERNAME_REGEX`. Another advantage is that for each setting not explicitly defined in your Django settings, the subclass will then use the corresponding default values. This behavior will be very handy in case you will need to override certain settings.

## Overriding default_settings

If down the line, you want to increase the login attempt limit to 100 every 15 minutes, and you only want SMS notifications for usernames with a “zz_” prefix, then you can simply modify your settings.py like so.

    # settings.py

    AUTH_LDAP_LOGIN_ATTEMPT_LIMIT = 100
    AUTH_LDAP_RESET_TIME = 15 * 60
    AUTH_LDAP_USERNAME_REGEX = r"^zz_.*$"

    AUTHENTICATION_BACKENDS = [
        # ...
        "mypackage.ldap.CustomLDAPBackend",
        # ...
    ]

If the `settings_prefix` of the subclass was also changed, then the prefix must also be used in your settings. For example, if the prefix was changed to “AUTH_LDAP_1_”, then it should look like this.

    # settings.py

    AUTH_LDAP_1_LOGIN_ATTEMPT_LIMIT = 100
    AUTH_LDAP_1_RESET_TIME = 15 * 60
    AUTH_LDAP_1_USERNAME_REGEX = r"^zz_.*$"

    AUTHENTICATION_BACKENDS = [
        # ...
        "mypackage.ldap.CustomLDAPBackend",
        # ...
    ]