title: Property '' does not exist on type 'Request<ParamsDictionary>'
body: <p>When trying to extend the <code>Request</code> interface from the package <code>express</code> to add some custom properties, I'm getting the following typescript error:</p>
  
  <p><code>TS2339: Property '' does not exist on type 'Request&lt;ParamsDictionary&gt;'.</code></p>
  
  <p>Do you know how to solve that?</p>