Populating database on Rails Port using osmosis authentication failure

Hi, I've been following the instruction on the github page for installing the Rails Port, and have successfully completed all of those instructions. I am now trying to populate the database following the instructions here. I've tried running the osmosis command:

osmosis --read-pbf [my-osm-file].osm.pbf --write-apidb host="localhost" database="openstreetmap" user="openstreetmap" password="" validateSchemaVersion="no"

However, it initially gives me an error that argument 7 (password) doesn't contain a value after the '=', so I removed that field. Now it is giving me a password authentication failed error for user "openstreetmap".

I tried manually logging into the openstreetmap database by running the following command:

psql -d openstreetmap -U openstreetmap

and I get this error:

psql: FATAL: Peer authentication failed for user "openstreetmap"

Running the same command but with my own username allows me to log into the database. So then I tried the osmosis command with the username replaced with mine, but it still gives me a password authentication failure error. I'm stuck now as to what to try next. Any suggestions would be very much appreciated.