I've been trying to make a simple iron-ajax post to the server, but it keeps failing at the preflight call. For the life of me I can't figure out what's going on, all the CORS headers seem to be correct on the server.
Response headers
Access-Control-Allow-Credentials:true
Access-Control-Allow-Headers:Content-Type
Access-Control-Allow-Methods:GET, POST, PUT, OPTIONS
Access-Control-Allow-Origin:*
cache-control:must-revalidate, private, no-cache, no-store, max-age=0
Connection:Keep-Alive
Content-Encoding:gzip
Content-Length:138
Content-Type:text/html
Request headers
Accept:*/*
Accept-Encoding:gzip, deflate, sdch, br
Accept-Language:en-US,en;q=0.8
Access-Control-Request-Headers:content-type
Access-Control-Request-Method:POST
Cache-Control:no-cache
Connection:keep-alive
The request is indeed made from localhost, but I would have thought that the * should take care of that.
Errors that are showing up in the console are:
OPTIONS https://... 403 (Forbidden) and
XMLHttpRequest cannot load https://.... Response for preflight has invalid HTTP status code 403
Any help/advice is appreciated.
The 403 response status indicates a general problem with the server backend not being configured to handle OPTIONS requests, not just CORS preflight OPTIONS requests.
The server must respond to OPTIONS requests with a 2xx success status—typically 200 or 204.
If the server doesn’t do that, it makes no difference what Access-Control-* headers you have it configured to send. And the answer to configuring the server to handle OPTIONS requests in the right way—to send a 200 or 204 success message—depends on what server software it’s running
来源：https://stackoverflow.com/questions/44966434/response-for-preflight-403-forbidden