How do you specify the ca cert when connecting to RDS via R Postgres?

    #https://cran.r-project.org/web/packages/RPostgres/README.html

    library(DBI)
    # Connect to a specific postgres database i.e. Heroku
    con <- dbConnect(RPostgres::Postgres(),dbname = 'DATABASE_NAME', 
                     host = 'HOST', # i.e. 'ec2-54-83-201-96.compute-1.amazonaws.com'
                     port = 5432, # or any other port specified by your DBA
                     user = 'USERNAME',
                     password = 'PASSWORD')

Trying to connect to the DB, but I get a ssl verification error because the remote DB is Aurora. is there a parameter to pass the SSL CA root?