title: allow user to login from only one pc
body: <p>In my WebApp that I was building with C# .net, i want to allow the user to connect only from one pc.
  so when the users logging-in in the first time i will save the pc details and when i will detect when its another pc they will not able to log in.</p>
  
  <p>What I was trying to do:</p>
  
  <p><strong>1)</strong> save the ip when the user first log-in and check it every login, <em>the problem:</em> the ip can be change.</p>
  
  <pre><code> protected string GetIPAddress()
  {
      System.Web.HttpContext context = System.Web.HttpContext.Current; 
      string ipAddress = context.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
  
      if (!string.IsNullOrEmpty(ipAddress))
      {
          string[] addresses = ipAddress.Split(',');
          if (addresses.Length != 0)
          {
              return addresses[0];
          }
      }
  
      return context.Request.ServerVariables["REMOTE_ADDR"];
  }
  </code></pre>
  
  <p><strong>2)</strong> save some key in local storage then to check the key every log in, <em>the problem</em>: they can clear the local storage or choose to not use it or the browser will not support local storage.</p>
  
  <pre><code>localStorage.setItem("key", "123123");
  </code></pre>
  
  <p>There is a good and safe way to do it?</p>