title: How to pass url param through amazon cognito hosted login
body: <p>I am using Amazon Cognito hosted login for my webapp and everything has been working great.  However, today I decided I wanted to pass a urlParam through the login flow.  The desired behavior is that a user goes to
  <code>https://example.com/?param1=foo</code>
  if they aren't logged in they go to the hosted cognito login page and when they go through the login flow and return to my site they go back to
  <code>https://example.com/?param1=foo.</code></p>
  <p>Unfortunately, if I try to add the ?param1=foo to the redirect_uri url param for the hosted login flow, I get an error like this, &quot;error?error=redirect_mismatch&quot; on the cognito signin page.</p>
  <p>Is there some way to set the callback url to allow for a url param?  Or is there another way to solve this problem?</p>