Using PG 10.7 and JDBC org.postgresql:postgresql:42.1.4
I had only a single slash between postgresql: and the host
jdbc:postgresql:/some.host.name:5432
I got
org.postgresql.util.PSQLException: FATAL: password authentication failed for user "some-name"
Naturally I tested and re-tested connecting manually as that user and with the supplied password. Eventually of course I started looking around a little more thoroughly...
I wonder if the message needs to be specifically about password authentication?