ASP.NET

<br />
<br />
...<br />
< credentials ><br />
  < user name="AAA" password="BBB" ><br />
  ...<br />
< /credentials ><br />
...<br />
<br />

protected void Login1_Authenticate(object sender, AuthenticateEventArgs e)
    {
        if (CheckAuthenticate(Login1.UserName, Login1.Password))
        {
            e.Authenticated = true;
            Response.Redirect("index.aspx");
        }
        else
        {
            e.Authenticated = false;
        }
        
    }

...
 public bool CheckAuthenticate(string user, string pass)
 {
     //My authentication checking logic
     //Query username and password from database for comparison with user  
     //and pass agument
 }