[[XBAuthentication sharedInstance] setHost:@"http://example.com"];

XBAuthentication *authenticator = [XBAuthentication sharedInstance];
authenticator.username = @"username";
authenticator.password = @"password";

[authenticator signup];
// OR, remember, OR, not AND
[authenticator signin];

// Forgot password (with username or email)
- (void)forgotPasswordForUser:(NSString *)user complete:(XBARequestCompletion)completion;

// Change password (with old / new password)
- (void)changePasswordFrom:(NSString *)oldPassword to:(NSString *)newPassword complete:(XBARequestCompletion)completion;

// save / load session, using for remember me function

- (void)saveSession;
- (void)loadSession;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    ...
    return [[XBAuthentication sharedInstance] application:application didFinishLaunchingWithOptions:launchOptions];;
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    [[XBAuthentication sharedInstance] applicationDidBecomeActive:application];
}

- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *)sourceApplication annotation:(id)annotation
{
    return [[XBAuthentication sharedInstance] application:application openURL:url sourceApplication:sourceApplication annotation:annotation];
}

[[XBAuthentication sharedInstance] startLoginFacebookWithCompletion:^(NSString *responseString, id object, int errorCode, NSString *description, NSError *error) {
    ... do anything that you want with responseString, object (response object), errorCode, description and error. all in your hand now.
}];