Re: scram and \password

On Tue, Mar 14, 2017 at 3:15 AM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:

> On 03/14/2017 04:47 AM, Tom Lane wrote:
>
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>
>>> I'm not talking about changing the default, just having it be possible
>>> to use \password with the new system as it was with the old, whatever
>>> exactly we think that means.
>>>
>>
>> Seems to me the intended behavior of \password is to use the best
>> available practice. So my guess is that it ought to use SCRAM when
>> talking to a >= 10.0 server. What the previous password was ought
>> to be irrelevant, even if it could find that out which it shouldn't
>> be able to IMO.
>>
>
> If the server isn't set up to do SCRAM authentication, i.e. there are no
> "scram" entries in pg_hba.conf,

The method is not part of the pg_hba matching algorithm, so either the
first match is scram, or it isn't. There is no fallback to later entries,
as I understand it.

> and you set yourself a SCRAM verifier, you have just locked yourself out
> of the system. I think that's a non-starter. There needs to be some more
> intelligence in the decision.
>

Right. And you can lock yourself out of the system going the other way, as
well, setting a md5 password when scram is in pg_hba. Which is how I ended
up starting this thread.

>
> It would be a lot more sensible, if there was a way to specify in
> pg_hba.conf, "scram-or-md5". We punted on that for PostgreSQL 10, but
> perhaps we should try to cram that in, after all.

So the backend for the incipient connection would consult the catalog
pg_authid before responding back to the client with an authentication
method, as opposed to merely pulling it out of pg_hba?

Cheers,

Jeff