# Broken Authentication (API2:2023)
In this vulnerability, due to insufficient security mechanisms for user authentication to access resources, there is a possibility of disruption and access to protected information by an attacker.

* Example

POST request for user login using authentication information:

```html
POST /api/login

Body:
{
  "username": "exampleuser",
  "password": "secretpassword"
}
```

### Non-compliant code (.NET)
```c#
// Non-compliant code
[ApiController]
[Route("api/[controller]")]
public class UserController : ControllerBase
{
  [HttpPost]
  public IActionResult Login(string username, string password)
  {
    if (AuthenticateUser(username, password))
    {
      // Generate and return authentication token
      var token = GenerateAuthToken(username);
      return Ok(token);
    }
    else
    {
      return Unauthorized();
    }
  }
  [HttpGet]
  public IActionResult GetUserData(int userId)
  {
    // Retrieve user data from the database
    var userData = Database.GetUserById(userId);

    // Return user data
    return Ok(userData);
  }

  // Other methods...
}
```


### Compliant code (.NET)
```c#
// Compliant code
[ApiController]
[Route("api/[controller]")]
public class UserController : ControllerBase
{
  private readonly IUserService _userService;
  private readonly IAuthenticationService _authenticationService;

  public UserController(IUserService userService,
IAuthenticationService authenticationService)
  {
    _userService = userService;
    _authenticationService = authenticationService;
  }

  [HttpPost]
  public IActionResult Login(LoginModel loginModel)
  {
    if (_authenticationService.AuthenticateUser(loginModel.Username,

loginModel.Password))

    {
      // Generate and return authentication token
      var token = _authenticationService.GenerateAuthToken(loginModel.Username);
      return Ok(token);
    }
    else
    {
      return Unauthorized();
    }
  }

  [HttpGet]
  [Authorize]
  public IActionResult GetUserData(int userId)
  {
    // Retrieve the authenticated user's identity
    var identity = HttpContext.User.Identity as ClaimsIdentity;
    if (identity != null)
    {
      // Get the user ID from the authentication token
      var userIdFromToken = identity.FindFirst("UserId")?.Value;

      if (!string.IsNullOrEmpty(userIdFromToken) && userIdFromToken == userId.ToString())

      {
        // Retrieve user data from the database
        var userData = _userService.GetUserData(userId);
        return Ok(userData);
      }
    }
    return Unauthorized();
  }

// Other methods...
}
```

## General prevention suggestions
* Use strong and standard authentication mechanisms such as JSON Web Tokens (JWT) or OAuth.
* Use strong encryption methods to store and transmit sensitive information, such as connection encryption (SSL/TLS).
* Validate authentication information and verify that each authentication request is from a valid user.
* Carefully check that authentication information (such as password) is secure and encrypted when transferring or storing data on the server.
* Using the limit of the number of failed attempts to log in and temporarily close the user account after a certain number of failed attempts.