How to have APM call an external API using a GET request?

In the irule, do I need to do anything special for the HTTPS connection to the LinOTP server? Examples I found are for HTTP.

You need to pass the traffic through an internal HTTP VIP and encrypt on the server side to the remote server. Sideband doesn't support SSL directly.

In the irule, how should I format the request - does the following look right?

That looks right.