This post outlines the development of a passwordless authentication solution using Xamarin and Twilio for SMS authentication. The solution involves creating a cross-platform mobile frontend in Xamarin that uses a feature of Xamarin called Xamarin.Forms, which allows writing user interface code in a shared project that generates UI for iOS, Android, and Windows Phone from the same source. The application sends a POST request with the user's phone number to validate the account, and then makes another POST request with the token received via SMS to authenticate the session. The solution uses ASP.NET MVC port of Ricky Robinett's Laravel backend, which provides endpoints for validating phone numbers and authenticating tokens. While the solution is complete, it lacks features such as registration pages, backup authentication methods, voice solutions, and profile pages, which could be added in future improvements.