Logs a user in using the :class:`~openstack_auth.forms.Login` form.

def login(request, template_name=None, extra_context=None, **kwargs):
    """Logs a user in using the :class:`~openstack_auth.forms.Login` form."""

    # If the user enabled websso and the default redirect
    # redirect to the default websso url
    if (request.method == 'GET' and utils.is_websso_enabled and
            utils.is_websso_default_redirect()):
        protocol = utils.get_websso_default_redirect_protocol()
        region = utils.get_websso_default_redirect_region()
        origin = utils.build_absolute_uri(request, '/auth/websso/')
        url = ('%s/auth/OS-FEDERATION/websso/%s?origin=%s' %
               (region, protocol, origin))
        return shortcuts.redirect(url)

    # If the user enabled websso and selects default protocol
    # from the dropdown, We need to redirect user to the websso url
    if request.method == 'POST':
        auth_type = request.POST.get('auth_type', 'credentials')
        if utils.is_websso_enabled() and auth_type != 'credentials':
            region_id = request.POST.get('region')
            auth_url = getattr(settings, 'WEBSSO_KEYSTONE_URL',
                               forms.get_region_endpoint(region_id))
            url = utils.get_websso_url(request, auth_url, auth_type)
            return shortcuts.redirect(url)

    if not request.is_ajax():
        # If the user is already authenticated, redirect them to the
        # dashboard straight away, unless the 'next' parameter is set as it
        # usually indicates requesting access to a page that requires different
        # permissions.
        if (request.user.is_authenticated and
                auth.REDIRECT_FIELD_NAME not in request.GET and
                auth.REDIRECT_FIELD_NAME not in request.POST):
            return shortcuts.redirect(settings.LOGIN_REDIRECT_URL)

    # Get our initial region for the form.
    initial = {}
    current_region = request.session.get('region_endpoint', None)
    requested_region = request.GET.get('region', None)
    regions = dict(getattr(settings, "AVAILABLE_REGIONS", []))
    if requested_region in regions and requested_region != current_region:
        initial.update({'region': requested_region})

    if request.method == "POST":
        form = functional.curry(forms.Login)
    else:
        form = functional.curry(forms.Login, initial=initial)

    if extra_context is None:
        extra_context = {'redirect_field_name': auth.REDIRECT_FIELD_NAME}

    extra_context['csrf_failure'] = request.GET.get('csrf_failure')

    choices = getattr(settings, 'WEBSSO_CHOICES', ())
    extra_context['show_sso_opts'] = (utils.is_websso_enabled() and
                                      len(choices) > 1)

    if not template_name:
        if request.is_ajax():
            template_name = 'auth/_login.html'
            extra_context['hide'] = True
        else:
            template_name = 'auth/login.html'

    res = django_auth_views.login(request,
                                  template_name=template_name,
                                  authentication_form=form,
                                  extra_context=extra_context,
                                  **kwargs)
    # Save the region in the cookie, this is used as the default
    # selected region next time the Login form loads.
    if request.method == "POST":
        utils.set_response_cookie(res, 'login_region',
                                  request.POST.get('region', ''))
        utils.set_response_cookie(res, 'login_domain',
                                  request.POST.get('domain', ''))

    # Set the session data here because django's session key rotation
    # will erase it if we set it earlier.
    if request.user.is_authenticated:
        auth_user.set_session_from_user(request, request.user)
        regions = dict(forms.Login.get_region_choices())
        region = request.user.endpoint
        login_region = request.POST.get('region')
        region_name = regions.get(login_region)
        request.session['region_endpoint'] = region
        request.session['region_name'] = region_name
        expiration_time = request.user.time_until_expiration()
        threshold_days = getattr(
            settings, 'PASSWORD_EXPIRES_WARNING_THRESHOLD_DAYS', -1)
        if expiration_time is not None and \
                expiration_time.days <= threshold_days:
            expiration_time = str(expiration_time).rsplit(':', 1)[0]
            msg = (_('Please consider changing your password, it will expire'
                     ' in %s minutes') %
                   expiration_time).replace(':', ' Hours and ')
            messages.warning(request, msg)
    return res