Synapse is a Matrix homeserver implementation developed by the matrix.org core team.
$ docker-compose run --rm synapse bash
>>> cd /data
>>> /start.py generate
>>> grep 'registration_shared_secret' homeserver.yaml
>>> exit
$ docker-compose up -d
$ docker-compose exec synapse bash
>>> cd /data
>>> register_new_matrix_user http://localhost:8008 -c homeserver.yaml --help
>>> sed -i '/registration_shared_secret/s/^/#/' homeserver.yaml
>>> exit
$ docker-compose restart