What methods and tools have you used to implement user identity verification systems?

To implement a user identity verification system in C#, several methods and tools are often used:

• Authentication via OAuth2/OpenID Connect — integration with external providers (Google, Microsoft, Facebook) using libraries such as Microsoft.AspNetCore.Authentication.
• Two-factor authentication (2FA) — adding a second level of verification, for example, via SMS, email, or code generator apps (Google Authenticator).
• Using ASP.NET Identity — a ready-made framework for managing users, roles, and authentication.
• User data validation — server-side validation of entered data to prevent forgery.

Example of a simple authentication using ASP.NET Identity:

var user = await _userManager.FindByNameAsync(username);
if(user != null && await _userManager.CheckPasswordAsync(user, password))
{
    // User successfully authenticated
}