How do you perform user authentication verification?

In C#, user authentication is often implemented using mechanisms like ASP.NET Identity or JWT (JSON Web Tokens). The process typically involves the following steps:

1. The user enters their login and password.
2. The server verifies these credentials by comparing them with stored data in the database (passwords are stored as hashes).
3. If the credentials are correct, the server creates a token (e.g., JWT) or sets an authentication cookie.
4. In subsequent requests, the server checks for the presence and validity of the token or cookie to confirm authenticity.

An example of creating a JWT in C# using the System.IdentityModel.Tokens.Jwt library:

var securityKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("secret_key"));
var credentials = new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha256);

var token = new JwtSecurityToken(
    issuer: "yourdomain.com",
    audience: "yourdomain.com",
    claims: claims, // list of user claims
    expires: DateTime.Now.AddHours(1),
    signingCredentials: credentials);

string tokenString = new JwtSecurityTokenHandler().WriteToken(token);

Thus, authentication boils down to validating the entered data and issuing a token that confirms the user is authorized.