Cross-origin resource sharing error: PreflightInvalidstatus in Azure Application API - azure

Question

I have backend Springboot API service which is running behind the Azure Application Gateway. The APIs are getting used in a Single page application. Spring boot APIs are well configured for CORS and working prefectly fine in ideal scenarios.
But getting CORS errror when Beackendend service is not responsive/down. I setup these values in Application gateway to deal with Preflight calls in case java service is not reachable.
Access-Control-Allow-Origin: {http_req_Origin}
Access-Control-Allow-Credentials: true
Access-Control-Allow-Methods: POST, GET, OPTIONS, DELETE, PUT
Access-Control-Allow-Headers: x-requested-with, authorization, content-type, unique-one-time-token
Access-Control-Max-Age: 1800
After doing these rewrite rules , there is still CORS error Cross-origin resource sharing error: PreflightInvalidstatus

Answer 1

See if any of the below can be workaround in your case
Make sure the request URL in your code isn’t missing a trailing
slash.
for example, you may need to add a trailing slash in your
code— e.g., http://localhost/api/auth/login/  or remove the slash
if present http://localhost/api/auth/login and try.
This may even happen sometimes when you try calling an https service as http, for example when you perform a request on :'http:// localhost/api/auth/login ' which might have to be be 'https:// localhost/api/auth/login
Or
You need to reply to that CORS preflight with the appropriate CORS
headers to make this work.
A CORS-preflight request is a CORS request that checks to see if
the CORS protocol is understood. It uses OPTIONS
as method and includes these  headers .You might need to reply to
that CORS preflight with the appropriate CORS headers.
References:
Fetch Standard (whatwg.org)
CORS#preflighted_requests
CORS