Getting username by userID without EBS

[BarryCarlyon]

@BarryCarlyon

The JWT from the extension is passed to the EBS
The EBS generates an App Access Token/Client Credentials token
And uses the UserID from the JWT + the App Access Token to lookup the user on the API.

You decode the JWT from your frontend, to extract the userID in the JWT.

You only need to generate a JWT if using Extension Pubsub or the Config Service.