How to configure customer-specific API keys for Azure Functions

Rory,

This is unfortunately not supported today. The authentication will happen based on key used and you can revoke/renew individual client keys, but that information is not currently surfaced to the functions.

There are some workarounds like mapping the keys by using the management API and matching the request key to identify the client, but they are cumbersome and inefficient.

I've had an issue tracking this here and I have just marked it for triage again to see if we can get this addressed soon.