title: Permit array in params
body: <p>I have the following JSON:</p>
  
  <pre><code>{
      "name": "pizza",
      "ingredients": [
          {"name": "tomato", "amount": 3, "unit": "un"},
          {"name": "chesse", "amount": 100, "unit": "gr"}
      ]
  }
  </code></pre>
  
  <p>And I pass this JSON using POST to my controller, then I need to trust this paramters but I'm not be able to permit the array of hash <code>ingredients</code>.</p>
  
  <p>How to permit it?
  I tried <code>params.permit(:ingredients).permit(:name, :amount, :unit).to_h</code>, but it doesn't work.</p>