All users can enter as one user "puser" without superuser priviledges: how?

I seek a simplistic access,

1. superuser "postgres" gets access when his system-name is "postgres",
but not otherwise [some security sought].
This can be done in pg_hba.conf with either
local all peer sameuser
local all trust #but anyone then gets "postges" access.

2. One other user, say "puser", gets access whatever his system-name.
The above
local all peer sameuser
disallows an arbitrary username entering as "psql template1 -U puser".
One can use
host all 127.0.0.1 255.0.0.0 ident jimsmap
then have pg_ident.conf with 1000 user entries like
jimsmap jameson puser
However, I seek a simpler method for numerous users,
each of whom will be granted access as user "puser".
ANY IDEAS?

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Jameson C. Burt, NJ9L Fairfax, Virginia, USA
jameson(at)coost(dot)com http://www.coost.com
(202) 690-0380 (work)