OPA Authorization with Envoy and X.509-SVIDs

Open Policy Agent (OPA) is an open source, general-purpose policy engine. The authorization provided by OPA (AuthZ) can be a good complement to the authentication that SPIRE offers (AuthN). This tutorial adds Open Policy Agent (OPA) to the SPIRE Envoy-X.509 tutorial to demonstrate how to combine SPIRE, Envoy, and OPA to perform X.509 SVID authentication and request authorization.