@Jakob :friendica:
Not sure how much more there is to say.
Install #Prosody as per usual, and use http_async for the auth method instead of "internal hashed".
I basically just reviewed the instructions for doing this with #eJabberd -> https://wiki.friendi.ca/docs/install-ejabberd (and adapted for Prosody - although I see now that they have actually included the prosody instructions there as well).

#Matrix Protocol Added to #Ejabberd

https://www.process-one.net/blog/matrix-protocol-added-to-ejabberd/

@Matt Panhans
for #ejabberd you can follow this: https://wiki.friendi.ca/docs/install-ejabberd

Mine is #Prosody. in prosody.cfg.lua I have this:

authentication = "http_async";
http_auth_url = "https://librenet.co.za/api/account/verify_credentials.json";