title: Antiforgery Token Cookie Not Appearing in Request Headers Only in when Embeded in Iframe
body: <p>I'm trying to embed a simple web app that will POST user input that is running asp.net Core 2.0 into an iframe.  The problem I am having is that while embedded, the request headers that are being generated lack the cookie header that contains the .AspNetCore.Antiforgery.[token].  It is being generated as expected outside of the iframe.</p>
  
  <p>This is causing a 400 error because the post is unable to validate the token.</p>
  
  <p>Request Headers generated outside of iframe:
  <a href="https://i.stack.imgur.com/vUuQm.png" rel="noreferrer">Request Headers: NO IFRAME</a></p>
  
  <p>Request Headers generated inside of iframe:
  <a href="https://i.stack.imgur.com/hHCQB.png" rel="noreferrer">Request Headers: INSIDE IFRAME</a></p>
  
  <p>Has anyone had this issue with the antiforgery token library?</p>
  
  <p>Thanks!!</p>