This module extracts profile details from the user’s vcard4 and provides them in the UserInfo endpoint of mod_http_oauth2 to clients the user grants authorization.
Whether this is really needed is unclear at this point. When logging in with an XMPP client, it could fetch the actual vcard4 to retrieve these details, so the UserInfo details would probably primarily be useful to other OAuth 2 and OIDC clients.
With the plugin installer in Prosody 0.12 you can use:
sudo prosodyctl install --server=https://modules.prosody.im/rocks/ mod_oidc_userinfo_vcard4
For earlier versions see the documentation for installing 3rd party modules