ios - Unable to change username value before login validation

Question

Where in the login process would I place code to set username before begin login with the delegate function

 - (BOOL)logInViewController:(PFLogInViewController *)logInController 
shouldBeginLogInWithUsername:(NSString *)username 
                    password:(NSString *)password

The think is i need unique usernames for my b2b app; which is for differents companies and this companies could have the same usernames. From the above, i set the username in pfuser to "company id"+"_"+"user id", and because that i try to set entered username by user on PFLogInViewController for login validation.

I make a custom subclass of PFLogInViewController:

#import "PFLogInViewControllerFSB.h"

@interface PFLogInViewControllerFSB ()

@end

@implementation PFLogInViewControllerFSB

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIColor *color = [UIColor lightGrayColor];
    self.logInView.usernameField.attributedPlaceholder = [[NSAttributedString alloc] initWithString:NSLocalizedStringFromTable(@"login_txt_user", @"Generales",nil) attributes:@{NSForegroundColorAttributeName: color}];
    self.logInView.passwordField.attributedPlaceholder = [[NSAttributedString alloc] initWithString:NSLocalizedStringFromTable(@"login_txt_password", @"Generales",nil) attributes:@{NSForegroundColorAttributeName: color}];
    self.logInView.logo = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 200, 50)];
    UILabel *labelLogo = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 50)];
    labelLogo.text = @"Catch Sales";
    [labelLogo setTextAlignment:NSTextAlignmentCenter];
    [labelLogo setTextColor:[UIColor lightGrayColor]];
    [labelLogo setFont:[UIFont fontWithName:@"Helvetica" size:30]];
    [self.logInView.logo addSubview:labelLogo];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

@end