The SDK Proxy service is a reverse proxy for the Certificate Manager clients. It allows CM clients to connect to the Certificate Factory (CF) service remotely over the internet without the need to expose the CF service externally. Requests from CM clients are forwarded to the CF service and responses are returned as if communicating directly with CF.
Since PGW itself uses CM SDK to communicate with the CF service it is possible to configure PGW to connect to another PGW which is running the SDK Proxy service. This is done by setting the cmhost configuration parameter in cm-gateway.properties to the URL of the SDK Proxy.
The CM SDK Proxy is transparent for clients, that is, a client communicates with CF in the same way no matter if it is via an SDK Proxy or not.