Have you had experience developing an authentication system from scratch?

Yes, I have experience developing an authentication system from scratch in C#.

The main steps included:

• Creating a user model with hashed passwords (for example, using PBKDF2 or BCrypt algorithms).
• Implementing registration and login mechanisms with data validation.
• Using tokens (such as JWT) for session management and authorization.
• Ensuring security against SQL injection, XSS, and CSRF.

An example of password hashing using Rfc2898DeriveBytes:

using System.Security.Cryptography;

public static byte[] HashPassword(string password, byte[] salt, int iterations = 10000)
{
    using var pbkdf2 = new Rfc2898DeriveBytes(password, salt, iterations, HashAlgorithmName.SHA256);
    return pbkdf2.GetBytes(32); // 256 bits
}

During authentication, I compared the hash of the entered password with the stored one. I also implemented issuing JWT tokens for subsequent requests.

This approach allows creating a secure and scalable authentication system without third-party libraries.