These are instructions to setup Postgres.app to allow connections over unix sockets. These instructions were written for macOS Sierra (10.12) and Postgres.app 9.6.0

1. Run Postgres.app once so that the configuration is initialized in `~/Library/Application Support/Postgres/var-9.6/`
2. Quit Postgres.app
3. Open `~/Library/Application Support/Postgres/var-9.6/postgresql.conf` in your favorite text editor
4. Uncomment the line `unix_socket_directories = '/tmp'` and change it to `unix_socket_directories = '/var/pgsql_socket,/tmp'`
5. Run `sudo mkdir -p /var/pgsql_socket`
6. Run `sudo chmod 770 /var/pgsql_socket`
7. Run `sudo chown root:staff /var/pgsql_socket`

*Note:* the config directory depends on the Postgres.app's major version…