Slack app Request URL for multi-org Salesforce integration , As I want to Distribute my App.

I have developed a Slack app that integrates with Salesforce. The app's Request URL currently points to my Salesforce Site endpoint, which processes Slack events using Apex. 

I plan to distribute this app to multiple customers. Each customer has their own Salesforce org and therefore their own Site URL. 

Since a Slack app supports only a single Request URL, how can a multi-tenant architecture be implemented?     What is the recommended approach for routing requests to the correct customer's Salesforce org after they install the app?