sslmode = TRUE/ALLOW/REQUIRE
sllmode = verify - ca

db <- dbConnect( dbDriver('PostgreSQL'), user = 'username', password = '*******.', dbname = 'dbname', host = 'host', port = 1234, sslmode='verify-full' )

Error in postgresqlNewConnection(drv, ...) : unused argument (sslmode = "verify-full")

db <- dbConnect( dbDriver('PostgreSQL'), user = 'USERNAME', password = '*****', dbname = 'DBNAME?ssl=true', host = 'HOST', port = 1234 )

con <- dbConnect(dbDriver('PostgreSQL'), dbname = 'dbname=DBNAME sslmode=require', host = 'HOST', port = 1234, user = 'USERNAME', password = 'PASSWORD')

Error in postgresqlNewConnection(drv, ...) : RS-DBI driver: (could not connect host on dbname "dbname": sslmode value "verify-full" invalid when SSL support is not compiled in )