login_version1.swift

func login() {
    
    do {
        let token = try loginUserWithUsername("konrad1977", password: nil)
        print("user logged in \(token)")
    } catch LoginError.EmptyUsername {
        print("empty username")
    } catch LoginError.EmptyPassword {
        print("empty password")
    } catch {
        print(error)
    }
}