App API authentication mechanism update

[phwizard]

Implement any updates to App authentication mechanism to support this scenario - i.e. 3rd party backend uses App ID and App Secret to generate their own JWT token to authenticate with our system.

Our backend verifies that JWT belongs to the correct App.

More details in forum here: https://forum.ethora.com/topic/22-integrating-ethora-chat-component-users-system-with-your-existing-legacy-system/

This is to support Use Case N3 as described here: https://forum.ethora.com/topic/21-chat-component-use-cases-for-users-authentication/