title: Append value to $request with add method
body: <p>I need to modify a field value which passed from login form in my controller and then use it, I searched in Stackoverflow and google and found the <code>add()</code> method for adding a value to <code>$request</code> so I trying to add a parameter to <code>$request</code>:</p>
  
  <pre><code>$number = '+' . $country-&gt;code . $request-&gt;mobile;
  $request-&gt;request-&gt;add(['number' =&gt; $number]);
  
  if ($this-&gt;attemptLogin($request)) {
          return $this-&gt;sendLoginResponse($request);
  }
  </code></pre>
  
  <p>but when I use <code>dd($request-&gt;all())</code> to test <code>$request</code>, the <code>number</code> does not exists in <code>$request</code> .</p>
  
  <p>What is the problem ?</p>