Verifying requests from Zendesk client app

Hi,

I have built a Zendesk client app which is communicating successfully with my back-end. 

I now want to verify the requests received by my back-end are coming from Zendesk. I have seen how you can specify a parameter in the manifest.json file and the client asks for this parameter on start-up.

However, I'm intending to submit the app to Zendesk's App Marketplace and wondering how it works when users are installing the app. I don't want them to have to enter a parameter on install. Is there another way to do this I'm missing?

Thanks