title: Swagger adding custom attributes to parameter definition
body: <p>We have a python web server app based on connexion and Flask libraries.
  For audit purposes we print every request, including request body, to the logs. Those logs are much more extensive than what Flask prints by default.</p>
  <p>However, there are parameters like passwords or keys that I don't want to print their values to the logs.</p>
  <p>I want to add custom attribute to several parameters' definition in swagger.yml so on web app start up I will get parameters definitions from connexion and save all the parameters that have this custom attribute, so later on I will hide values of those parameters in the logs.</p>
  <p>My desired definition:</p>
  <pre class="lang-yaml prettyprint-override"><code>    paths:
        /demo_add_user:
          post:
            summary: &quot;add user&quot;
            operationId: api.api.demo_add_user
            parameters:
              - name: &quot;new_user&quot;
                in: body
                required: true
                description: &quot;Use to add&quot;
                schema:
                  $ref: &quot;#/definitions/NewUser&quot;
              - name: &quot;password&quot;
                in: body
                description: &quot;user password&quot;
                required: false
                type: string
                x-hidden: true
            responses:
  </code></pre>
  <p>Obviously, I would like connexion to ignore this attribute since this is specific to our implementation.
  Any way to add custom attribute like <code>x-hidden</code> to parameter definition?</p>