If we need to add any configuration at Atom/Environment level, we will create Custom policy file in bin folder parallel to HIGH Policy file using procrunner-CUSTOM.policy and procworker-CUSTOM.policy file names.
If you are getting any kind of Domain Protection Error, we need to add below line to get that resolved in Custom Policy.
permission java.lang.RuntimePermission "getProtectionDomain";
For database access -
permission java.net.SocketPermission "*:1433", "connect,resolve";