Help with authentication on Debain/Ubuntu installation

I am trying to set up to do some work with pg_dump, and I would like to be
able to connect from my normal user to do this. This is on a Ubunt 18.04
installation. I have added the follwing to pg_hba.conf:

host    all             all             0.0.0.0/0               md5
hostssl all             all             0.0.0.0/0               md5

But when I try to login like this:

psql stan postgres -W

I get the following error, and yes, I set postgres'es password to something
I know:

tan@stantest:~$ psql stan postgres -W
Password: 
psql: error: could not connect to server: FATAL:  Peer authentication
failed for user "postgres"
stan@stantest:~$ 

What am I doing wrong?


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"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
						-- Benjamin Franklin