Example of basic authentication situation

BasicLoginExample.swift

// MARK: LoginViewController

class LoginViewController: UIViewController {

    func login(with username: String,
               password: String) {
        let authenticationSession = AuthenticationSession()
        authenticationSession.performLogin(with: username,
                                           password: password)
    }
}

// MARK: AuthenticationSession

class AuthenticationSession {
    
    func performLogin(with username: String,
                      password: String) {
        let userIdentifier = Service.login(username, password)
    }
}