I fail to see how ident over TCP is insecure when used on the localhost address. Can you explain? Otherwise, is there a way to make peer authentication work with TCP connections?
ident is secure (or as secure as 'peer' for unix sockets) over TCP/IP loopback connections. But pretty much only then or on networks that you totally control all hosts on and all access to.
To spoof ident you must be able to open a listening socket on a privileged port on the loopback host. So you need superuser privileges or the CAP_NET_BIND_SERVICE capability which must be explicitly granted.
I am not arguing for ident to be removed. I'm arguing for it to stop being the default for rpm package initdb, since it's totally useless and nonfunctional without additional services that the rpms do not depend on. It actively gets in the way of users since they cannot then simply
CREATE USER foo WITH PASSWORD 'bar';
and connect. They have to go in and unf@#$ our generated pg_hba.conf too.
So if you like ident, fine. That's not a problem. You can
/usr/pgsql-12/bin/postgresql-12-setup -A ident
and nothing else changes for you. But it's a really obsolete and unhelpful default, and it's also one that adds yet another difference vs the Debian packages to add to user confusion.
[craig@ayaki] $ psql -h localhost
psql: error: could not connect to server: FATAL: Ident authentication failed for user "craig"
"WOT?"
Now, we're hardly going to depend on the ident service in the packages. It's a security policy violation in many places to even run it. So we should change the default - probably to scram-sha-256 on pg11 and pg12, and md5 on older releases.
The only BC implication I can see is that someone's scripts might, rather than invoking
/usr/pgsql-12/bin/postgresql-12-setup -A md5
be doing
/usr/pgsql-12/bin/postgresql-12-setup
sed -i 's/ident/md5/g' /var/lib/pgsql/12/data/pg_hba.conf
or the like. But I don't think that's a big concern: it's an easy fix, only affects new initdb's, and is sufficient to cover in the 'news' section + changelog.