I'm doing research for a new Slack app that will require the admin adding the app to paste an API token and request url for the third-party API which the app will call. I can't find anywhere in the Slack API docs to store these settings on an app-wide basis. Can this be done via environment variables of some type?
Slack Apps don't really store settings like that. You would need to persist them in a data store of your choice, like MySQL, Dynamo etc and access them from your code.