Re: can't get psql authentication against Active Directory working

Greetings,

* Tomas Pospisek (tpo2(at)sourcepole(dot)ch) wrote:
> again thanks a lot for trying to help me!

Sure, would like to see it work for you.

> On 21.02.23 16:29, Stephen Frost wrote:
> > * Tomas Pospisek (tpo2(at)sourcepole(dot)ch) wrote:
> > > On 20.02.23 15:17, Stephen Frost wrote:
> > > > * Tomas Pospisek (tpo2(at)sourcepole(dot)ch) wrote:
> > > > > so I'm trying to authenticate psql (on Windows) -> postgres (on Linux) via
> > > > > Active Directory.
> > > >
> > > > Looks like you're trying to do a bit more than that as you're using
> > > > GSSAPI (not SSPI, which would be the more typical method on Windows..)
> > > > and you're asking for an encrypted connection. Is there a reason you're
> > > > going down this particular route..?
> > >
> > > The reason I'm using the GSSAPI is it's the only documented way to do
> > > authentication from psql.exe against Active Directory that was able to find.
> >
> > I mean ... https://www.postgresql.org/docs/current/sspi-auth.html
>
> Were should the settings that are discussed in that document be configured?
> In pg_hba.conf?

Yes, it's in that part of the documentation. Note that you may not need
to actually configure any of those options..

> That document says:
>
> "SSPI authentication only works when both server and client are running
> Windows, or, on non-Windows platforms, when GSSAPI is available."
>
> I interpret that phrase like this:
>
> * there's a case where both server and client are running Windows (doesn't
> apply to me)
> * there's a case where both are running non-Windows (doesn't apply to me
> either - server is Linux, client is Windows)
>
> So that's an extremely terse docu that is not clear at all to me.
>
> I'd suggest to change that phrase into:
>
> "SSPI authentication works when both server and client are running Windows.
> When server or client are on non-Windows platforms then those need to use
> GSSAPI."
>
> - assuming that my interpretation of that super terse docu is correct of
> course.

No, that's not correct. The blog post that I referenced is actually
using SSPI on the client and GSS on the server and it works because
they're compatible with each other on the wire. Perhaps we could
improve the documentation you reference above but it's not actually
wrong as-is. Perhaps this would be clearer:

SSPI and GSS are wireline compatible and can be mixed and matched
between clients and servers (where support for GSS is built into the
client library or the server), provided that there is an encryption
method which both will accept.

The encryption method bit is more of a historical artifact at this
point as modern systems have compatible AES-based encryption methods,
but that wasn't always the case. It's also possible that it'll become
an issue in the future but at least for the moment most installations
have an AES-based compatible encryption method.

> > > Even now I am unable to find *any* documentation on how to go about doing
> > > auth from psql.exe to AD with SSPI. Would you have any pointers to
> > > documentation or a howto (or a blog post or a stackoverflow answer or...).
> >
> > Sure, here's a blog post that I wrote about doing exactly that:
> >
> > https://www.crunchydata.com/blog/windows-active-directory-postgresql-gssapi-kerberos-authentication
>
> Note that that document doesn't mention SSPI a single time.

It doesn't actually need to because SSPI is the default and it all just
works.. I suppose I could have added in somewhere "SSPI is used on the
client for this", perhaps, but the blog post was more focused on "this
is what you do to make it work" and you don't really need to know that
the API that the client is using in this case happens to be called SSPI.

> The ultra terse Postgres docu is using terms such as "SAM", "negotiate
> mode", "UPN", without a reference to their definition, which leaves to
> Windows noobs like me (and equaly Windows non-noobs) without a clue.

I'm certainly all for improving the documentation. Not sure that just
spelling those out would really be enough and I'm rather confident that
trying to explain all of how Kerberos and AD work wouldn't really be
maintainable in our documentation. Still, specific suggestion on how we
can improve would be great.

> Searching "kerberos SAM" or "SSPI negotiate mode" on duckduckgo doesn't seem
> to lead to useful hits. So the documentation seems to be geared to experts
> of both Kerberos and Active Directory and Windows technology alike which as
> far as I can tell is a very rare specimen.

Active Directory experts certainly should be generally familiar with
Kerberos (and the terms you reference above are actually all AD ones,
really..), so I'd argue that the documentation is mainly focused on
helping those individuals. I do generally agree that it would be good
if there were more folks out there who understood this stuff. I'm not
sure how to go about making that happen though.

> > > The reason I am apparently asking for encrypted communications is that I
> > > apparently misinterpreted what `gssencmode`: I thought that it would force
> > > the use of GSS but apparently it's forcing a connection encryption?
> >
> > gssencmode indeed requires a GSS encrypted connection. Unfortunately,
> > there isn't a way to force GSS or SSPI be used for authentication today
> > (outside of GSS with encryption) from the client side, though that's
> > something that's been discussed and I think most people feel would be
> > good to have. That said, if the server is configured in pg_hba for gss
> > (or sspi), then the client will try to authenticate that way.
>
> As far as I can see it is *not possible* to configure the server for SSPI
> ("or sspi")? It's only possible to configure it for GSS *and* SSPI at the
> same time (?) assuming the server is running on a non-Windows platform?

As I mention above, on the wire GSS and SSPI are compatible, so a server
on a non-Windows platform configured with GSS is also going to work for
clients using SSPI (and, indeed, the server isn't really going to even
directly be able to tell that the client is using SSPI..).

Maybe I can explain this a bit better-

GSS and SSPI are *APIs* into the respective Kerberos libraries on those
systems. You can consider what's spoken on the actual wire between the
systems to be 'generic Kerberos'.

> > Hopefully the blog post and this discussion helps you make some
> > progress. I wonder how close you are to everything working if you'd
> > just drop the 'gssencmode' setting, or maybe explicitly set it to
> > 'disable'...
>
> We dropped the gssencmode setting and were still getting the "Internal
> credentials cache error" error. That said, I'll have another session on
> probably Monday and I'll try to start from scratch, use the psql.exe that is
> coming with vanilla QGIS (without GSS support) (and not the one from OSGeo
> with compiled in GSS support) so that it absolutely should use SSPI and not
> use GSS at all.

Hrmpf. That's certainly curious that it still gave you that error..
Was it also still trying to call out to the MIT Kerberos For Windows
services? I wonder if maybe somewhere else the gssencmode was still
getting picked up as being set..

> Hopefully that will work. Wish me luck :-D! Thanks a lot for helping
> Stephen!!!

Sure, looking forward to hearing what happens next.

Thanks!

Stephen