[maynman]

If you're a heathen like me, you sometimes store JSON configuration in environment variables https://mitchum.blog/how-to-store-json-in-an-environment-var...

[arethuza]

Storing the name of an "environment" in an environment variable and then using that to pick the appropriate configuration file is what .Net Core does for web apps and that seems to work fairly well.

Then, of course, you have the fun of Azure Application Configuration and KeyVaults - which are fine once set up and your app is happy with them.