login with facebook

gistfile1.swift

func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {
        if let error = error {
            print(error.localizedDescription)
            return
        }
        
        if !result.isCancelled {
            let credential = FIRFacebookAuthProvider.credential(withAccessToken: FBSDKAccessToken.current().tokenString)
            FIRAuth.auth()?.signIn(with: credential) { (user, error) in
                if let error = error {
                    print(error.localizedDescription)
                    /*
                    [AnyHashable("error_name"): ERROR_EMAIL_ALREADY_IN_USE, 
                    AnyHashable("FIRAuthErrorUserInfoEmailKey"): email@example.com, 
                    AnyHashable("NSLocalizedDescription"): The email address is already in use by another account.]
                    */
                }
            }
        }
    }