The client needs a ca .pem certificate to check the SSL/TLS certificate presented by the PostgreSQL server:
https://vertx.io/docs/vertx-pg-client/java/#_using_ssl_tls

Add an option to the PostgreSQL configuration that contains that ca .pem certificate.
If that option is used the module requires a SSL/TLS connection and a valid server certificate when connecting to PostgreSQL by setting sslmode=verify-full.

Required unit tests:
If the option is set:

• Connection is rejected if connection is unencrypted.

• Connection is rejected if connection uses SSLv2Hello, SSLv3, TLSv1, TLSv1.1 or TLSv1.2 (only TLSv1.3 is allowed)

• Connection is rejected if server certificate is valid but is not issued for the hostname configured in DB_HOST