title: Extra Query String Params Appearing from Form Submission
body: <p>I noticed that when performing a <code>POST</code> request from certain sites, it passes along my form data (normal) and some extra params in a query string. These extra params are not coming from hidden form inputs and appear to be somewhat random. For example, if you go to the American Airlines homepage and click on the search button, it sends a <code>POST request to /find-flights</code> with extra form data keys <code>X-6LdxA4pr-uniqueStateKey, X-6LdxA4pr-b, X-6LdxA4pr-c, X-6LdxA4pr-d, and X-6LdxA4pr-a.</code> The script code responsible for this seems to have been rendered unreadable and is at the start of the page.</p>
  
  <p>How is this possible? I thought the form data was generated only from the form element at the time of submission. I tried to find documentation detailing how exactly the query string is generated, but nothing would explain these extra params. They appear to be locally generated since there are no requests in between pressing the button and the POST request. </p>