“CAUTION: provisional headers are shown” in Chrome debugger

Question

I noticed a strange caution message when looking at downloaded resources using Google chrome inspector (F12):

Caution provisional headers a

Answer 1

I encountered this issue, and I managed to identify a specific cause, which isn't mentioned above either in answers or the question.

I am running a full js stack, angular front end and node back end on SSL, and the API is on a different domain running on port 8081, so I am doing CORS requests and withCredentials as I am dropping a session cookie from the API

So specifically my scenario was: POST request, withCredentials to port 8081 caused the "CAUTION: provisional headers are shown" message in the inspector and also of course blocked the request all together.

My solution was to set up apache to proxy pass the request from the usual SSL port of 443 to the node SSL port of 8081 (node has to be on a higher port as it cannot be ran as root in prod). So I guess Chrome doesn't like SSL requests to unconventional SSL ports, but perhaps their error message could be more specific.