Free. Cross-platform. Open source.
A framework for building web apps and services with .NET and C#.
Supported on Windows, Linux, and macOS
ASP.NET supports industry standard authentication protocols. Built-in features help protect your apps against cross-site scripting (XSS) and cross-site request forgery (CSRF).
ASP.NET provides a built-in user database with support for multi-factor authentication and external authentication with Google, Twitter, and more.