CORS stands for Cross-origin Resource Sharing, it's a mechanism to allow a server resources to be requested by another entity outside this server's domain. The CORS mechanism is involved in a Sodius OSLC Adapter for PTC Windchill because resources provided by your CLM serverr(s) will be requested by the PTC Windchill server and vice-versa.
In some cases, you may think your CORS setup is correct, but CORS issues still remain. This may be due to the use of proxy server between the different parties of a whole Sodius OSLC Adapter for PTC Windchill server.
So if your company is running a proxy server to access the Jazz CLM server, do the following to allow your Sodius Adapter and PTC Windchill to "see" your CLM: