Binds to the LDAP server with AUTH_LDAP_BIND_DN and
        AUTH_LDAP_BIND_PASSWORD.

def _bind(self):
        """
        Binds to the LDAP server with AUTH_LDAP_BIND_DN and
        AUTH_LDAP_BIND_PASSWORD.
        """
        self._bind_as(self.settings.BIND_DN, self.settings.BIND_PASSWORD, sticky=True)