I am trying to access NIFI rest api of another server from my machine using ajax like below,
url:"https://serverip:port/nifi-api/",
{Authorization : 'Bearer ' + 'access token here'}
Getting Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource error.
Apache NiFi's API is designed to be invoked by a variety of clients, but in this case I think you are encountering a security precaution put in place by CORS (Cross-Origin Resource Sharing).
If a piece of code on server A (your non-NiFi machine) makes an AJAX request to a different origin (your NiFi instance), and the HTTP method is not GET (and some other minor restrictions), server A will first send a "preflight" request, which is HTTP OPTIONS, to the remote instance to determine what requests are valid. A server can reply to this with the header Access-Control-Allow-Origin: *, which is a wildcard value denoting it accepts requests from any origin. However, if you want to send credentials along with the request, the originating hostname must be explicitly listed in the response (Access-Control-Allow-Origin: https://serverA.com).
Because NiFi uses an embedded Jetty server to host the API, you may have to explicitly add a CrossOriginFilter as described here.