Only technote I could find that mentioned tango.policy was technote 1286604 but that wasn’t it. I did however find a clue in the Lotus Connections wiki and was able to adapt it to my needs.
<Application server (e.g. server1)>Java and Process ManagementProcess DefinitionJava Virtual MachineCustom Properties
java.security.auth.policy -> <path to communities.policy file>