Values:
SSL_MODE_UNSPECIFIED (0):
SSL mode not specified. Defaults to SSL_MODE_ALLOW.
SSL_MODE_ALLOW (1):
SSL connections are optional. CA verification
not enforced.
SSL_MODE_REQUIRE (2):
SSL connections are required. CA verification
not enforced. Clients may use locally
self-signed certificates (default psql client
behavior).
SSL_MODE_VERIFY_CA (3):
SSL connections are required. CA verification
enforced. Clients must have certificates signed
by a Cluster CA, e.g. via
GenerateClientCertificate.