Re: [HACKERS] SCRAM authentication, take three

On 04/14/2017 10:33 PM, Peter Eisentraut wrote:

On 4/11/17 01:10, Heikki Linnakangas wrote:

That question won't arise in practice. Firstly, if the server can do
scram-sha-256-plus, it presumably can also do scram-sha-512-plus. Unless
there's a change in the way the channel binding works, such that the
scram-sha-512-plus variant needs a newer version of OpenSSL or
something. Secondly, the user's pg_authid row will contain a
SCRAM-SHA-256 or SCRAM-SHA-512 verifier, not both, so that will dictate
which one to use.

Right.  So putting the actual password method in pg_hba.conf isn't going
to be useful very often.

I think the most practical thing that the user wants in pg_hba.conf is
"best password method supported by what is in pg_authid".  This is
currently spelled "md5", which is of course pretty weird.  And it will
become weirder over time.

I think we want to have a new keyword in pg_hba.conf for that, one which
does not indicate any particular algorithm or method (so not "scram" or
"sasl").

We could use "password".  If we think that "md5" can mean md5-or-beyond,
then maybe "password" can mean password-or-md5-or-beyond.

Or otherwise a completely new word.

We also want to give users/admins a way to phase out old methods or set
some policy.  We could either make a global GUC setting
password_methods='md5 scram-sha-256' and/or make that an option in
pg_hba.conf past the method field.

Yeah, that would be reasonable. It can't be called just "password", though, because there's no way to implement "password-or-md5-or-scram" in a sensible way (see my reply to Simon at [1]). Unless we remove the support for what "password" does today altogether, and redefine "password" to mean just "md5-or-beyond". Which might not be a bad idea, but that's a separate discussion.

In any case, I think we would probably still need more fine-grained control, too, so we would still need to have "scram-sha-256" as a method you can specify directly in pg_hba.conf. So I consider this as a separate, new, feature that we can add in the future, if it seems worth the effort.