This is a fail in the documentation/spec side. It still functions in v2.
sip_auth is a valid option to pass into the start function of freeswitch_media_manager. Enabling the manager from the admin gui presents a checkbox to enable integration. The options are passed to the fetch handler process. When a sip registration request comes in, Freeswitch will ask OpenACD for information. OpenACD then checks it's list of currently logged in agents, generates an A1 hash and returns it.
The caveat is that when sip_auth is enabled on freeswitch_media_manager, registrations are rejected unless there is a matching agent logged in.
Micah