title: How to do POST request in Codeception FunctionalTest with JSON Body
body: <p>Im using Codeception with Yii2. I need to do a POST request with json content body. I dont want to use REST module cause have not even been able config it yet. (Thats a longer story...)</p>
  
  <p>I have been able to write my GET tests fantastic. Now with the first POST test, Im stuck.</p>
  
  <ol>
  <li>There is a <code>$I-&gt;amOnPage([])</code> method in Functional Test which can only do GET request. </li>
  <li><code>sendAjaxPost</code> does not allow sending content body with POST.</li>
  <li><code>$I-&gt;sendPOST('api/xyz',"{\"xyz\":1}")</code> also did not work cause Yii did not get any route so instead loaded the homepage. The path got lost in the call stacks.</li>
  <li>There is a <code>InnerBrowser-&gt;_loadPage</code> method which allows me to do a request with all configurable way but I cannot find a way to access it.</li>
  </ol>
  
  <p>Any way to get access to <code>InnerBrowser</code> object from the test?
  I have tried <code>$I-&gt;getModule('PhpBrowser')-&gt;_loadPage</code> or <code>$this-&gt;getModule('Yii2')</code></p>