This script must be installed on ejabberd server.
External authentication should call index.js.
Add hosts and API url in config.authServiceUrls (see example config).
Example ejabberd config:
host_config:
"localhost":
auth_method: [external]
extauth_program: "node /opt/ejabberd/xmpp-auth/index.js"
extauth_pool_size: 5
auth_use_cache: false