/**
 * An apex page controller that exposes the site login functionality
 */
global with sharing class CommunitiesLoginController {

    global CommunitiesLoginController () {}

    // Code we will invoke on page load.
    global PageReference forwardToAuthPage() {
        String startUrl = System.currentPageReference().getParameters().get('startURL');
        String displayType = System.currentPageReference().getParameters().get('display');
        return Network.forwardToAuthPage(startUrl, displayType);
    }
    // Code we will invoke on page load.
    global PageReference forwardToCustomAuthPage() {
        return new PageReference('/CustomLoginPage');
    }
}

/**
 * An apex page controller that exposes the site login functionality
 */
@IsTest global with sharing class CommunitiesLoginControllerTest {
    @IsTest(SeeAllData=true)
    global static void testCommunitiesLoginController () {
        CommunitiesLoginController controller = new CommunitiesLoginController();
        System.assertEquals(null, controller.forwardToAuthPage());
        PageReference p = new PageReference ('/CustomLoginPage');
        System.assertEquals( p, controller.forwardToCustomAuthPage());
    }
}