This module implementing XEP-0215 is included with Prosody 0.12 but made available here for older versions.
Documentation is available on the Prosody site.
With the plugin installer in Prosody 0.12 you can use:
sudo prosodyctl install https://modules.prosody.im/rocks/mod_external_services-5-1.src.rock
For other see the documentation for installing 3rd party modules