PostgreSQL force sslmode=verify-full
Maybe you want to limit the clients to those which present a given certificate, as described in Using client certificates:


  To require the client to supply a trusted certificate, place
  certificates of the certificate authorities (CAs) you trust in the
  file root.crt in the data directory, set the parameter ssl_ca_file in
  postgresql.conf to root.crt, and set the clientcert parameter to 1 on
  the appropriate hostssl line(s) in pg_hba.conf


On the other hand, sslmode=verify-full is a client-side feature. It benefits a client by ensuring that it connects to the intended server. It does not benefit a server as it's the server that is being checked.

Having a server being configured to "refuse to not being checked" doesn't seem to make much sense, as if a server would say "I don't trust myself".