rely on .pgpass w/ "create user mapping"

I am trying to create a script which creates a postgres-fdw connection between two postgres 9.4 databases. The script (which is checked in under version control), has been relying on pgpass to do other things. Is there any option I can use to request that the password be looked up in pgpass? ... in general, where is the documentation on what options are available for "CREATE USER MAPPING"? the reference just says that options depend on the server.