Custom Secret Plugin - Communicate with other Secret Engines


I implemented a custom (secret) plugin. My only issue is that I need to communicate with other replications of the (same) plugin, in the system.

For example, say that I deployed the plugin as PluginA and PluginB. One way to do this, would be to communicate with any other instance of it through HTTPs (like an API), but I don’t really like this solution. I mean, it should be some other way to access the core system and then the instance of, say, PluginB. I searched for examples (like, how the Cubbyhole is accessed by other Secret Engines etc.), but I didn’t really find anything useful.

Edit: Another example would be:
Say that I have a user that has some private data under a KV engine (e.g., usersName/privateData). This user invokes a function of PluginA, but pluginA needs to fetch some (private!) data that exist under the afforementioned KV engine. So, how can this user feed the custom plugin with his private data?

Any suggestions or ideas?