Obtain unique client ID in Forge app

I’m writing a Forge app that needs to save some data in an external MySQL database. I’ve got the backend up and running in Heroku and the frontend working just fine in Jira using the forge/fetch API. What I’m after is the best way to obtain a unique internal client ID. I can get the baseUrl through rest but this is slow and I’m not sure will always be accurate. Any ideas?