title: Browser won't set ASP.NET_SessionId cookie on payment gateway's post request to our site
body: <p>We're experiencing a weird problem with the payment process of our web application which results in loss of session data.</p>
  
  <p>In this process, after our check-out page user is redirected to payment provider's page and redirected back to our site (to a url we specify) as soon as s/he's done there. This last redirect is done by browser's evaluation of the payment provider's html code which basically consists of a form that posts to our site and a few lines of javascript code that posts that form on page load. At this point browser makes the post request but does not set the "ASP.NET_SessionId" cookie which is present in the previous requests made to the exact same domain (our application's domain). What's more weird is that it sets another cookie we use named "AcceptCookie". It just simply chooses to drop "ASP.NET_SessionId" cookie.</p>
  
  <p>To illustrate the situation I took some screenshots. (In these screenshots orange and green rectangles contain exactly the same value.)</p>
  
  <ol>
  <li>This is the request that made (to our application) when user presses "Check Out" button. After this request user is redirected to payment provider's page.</li>
  </ol>
  
  <p><a href="https://i.stack.imgur.com/PzDfn.png" rel="noreferrer">check-out request</a></p>
  
  <ol start="2">
  <li>This is the final page that is served by payment provider after user is done there. As you can see it's just a simple form that is automatically posted to our domain on page load.</li>
  </ol>
  
  <p><a href="https://i.stack.imgur.com/FsXu7.png" rel="noreferrer">payment provider's final response</a></p>
  
  <ol start="3">
  <li>But this post request does not include "ASP.NET_SessionId" cookie which results in acquiring a new session id and the loss of previous session data. And again, just "ASP.NET_SessionId" is missing, not the other one named "AcceptCookie".</li>
  </ol>
  
  <p><a href="https://i.stack.imgur.com/ZByVc.png" rel="noreferrer">post request that brings the user back to our site (made with javascript in the previous step)</a></p>
  
  <p>Finally we figured that on the older versions of browsers this problem does not occur. On Firefox 52 it works like a charm but on Firefox 71 the above problem happens.</p>
  
  <p>Any ideas?</p>
  
  <p>Note: It's an ASP.NET MVC application with targetFramework="4.5.2"</p>
  
  <p>Have a nice day.</p>