title: FederatedAuthentication CanReadSignInResponse causes a potentially dangerous request
body: <p>I have an action with</p>
  
  <pre><code>[HttpPost]
  [ValidateInput(false)]
  public ActionResult Foo()
  {
      var module = FederatedAuthentication.WSFederationAuthenticationModule;
  
      // exception in the line bellow
      if (module.CanReadSignInResponse(System.Web.HttpContext.Current.Request, true))
      {
      }
  }
  </code></pre>
  
  <p>When I call the method it throws an exception saying the request is potentially dangerous. We send a XML on the post.</p>
  
  <p>Stack trace:</p>
  
  <p><img src="https://i.stack.imgur.com/Hfrtl.png" alt="stacktrace"></p>
  
  <p>Even with the attribute <code>[ValidateInput(false)]</code> on the action this exception occurs.</p>
  
  <p>Any idea why it happens? Is there a way to prevent it?</p>