Check Returning Registered Users Exist in User Account Service

[noce2]

• Auth0 makes a GET call to search for a user via the /organisations/{}/users endpoint prior to returning a token to the web UI
• Auth0 adds the appropriate permissions returned in the response from the User Account Service to the IDToken as a custom scopes
• Auth0 appropriately handles any user search failures as per login flow diagram
• Auth0 makes calls to the User Account Service via the API Gateway with an API Key