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

Greetings,

* 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..?

> psql (Linux) -> postgres (Linux) with authentication against Active
> Directory does work.

That's good. One thing to know about Linux vs. Windows when it comes to
Kerberos (and GSSAPI/SSPI) is that the default service name is different
between them. See the libpq parameter krbsrvname documentation here:

https://www.postgresql.org/docs/current/libpq-connect.html

> However the same with psql.exe on Windows does not. I get:
>
> D:\>C:\OSGeo4W\bin\psql.exe service=the_db
> psql: error: connection to server at "dbserver.example.lan
> (192.168.4.104), port 5432 failed: could not initiate GSSAPI
> security context: No credentials were supplied, or the credentials
> were unavailable or inaccessible: Internal credentials cache error

That's a bit of an odd message to get if krbsrvname is this issue
though.

> psql.exe from the OSGeo4W QGIS Installer *does* include GSS support. (I have
> tried with a different psql.exe without GSS support and it would tell me
> that it does not support GSS).

Providing the specific messages would possibly be helpful here..

> The .pg_service.conf file in the users $HOME directory looks like this:
>
> [the_db]
> host=dbserver.example.lan
> port=5432
> user=user(at)EXAMPLE(dot)LAN
> gssencmode=require
>
> This same pg_service.conf does work for psql (Linux).
>
> Also getting a Kerberos ticket for the service on Windows does work:
>
> D:\> klist get postgres/dbserver(dot)example(dot)lan(at)EXAMPLE(dot)LAN
> [...]
> This will list the ticket

Is this using MIT klist or Windows klist though?

> But when using psql.exe it will not get a ticket for the service nor will it
> apparently use the existing service ticket.

As mentioned above, GSSAPI and SSPI aren't the same thing and what I
suspect you're seeing here is that the Windows klist is using SSPI but
the psql you have is built with GSSAPI. There used to be a Kerberos For
Windows utility that would make the bridge between those two, as I
recall, put out by MIT but I'm not sure what the current state of it is.
It hasn't been needed for a very long time as SSPI generally works fine-
though we don't yet have SSPI support for encryption.

> I have tried to trace psql.exe with Window's Process Monitor and I can't see
> it accessing no keytab file (I'm not sure whether a keytab file exists at
> all under Windows or if psql.exe doesn't instead need to access some Windows
> service). I see that psql.exe will open and close a TCP connection to
> dbserver.example.lan, however as far as I can see that connection is
> completely irrelevant for the aquisition of a Kerberos ticket for the
> service since that is a business purely between psql.exe and Active
> Directory or respectively between psql.exe and the credentials cache. And
> there is no other TCP connection being opened to anywhere from psql.exe.
>
> What I find suspicious about the error above is "... the credentials were
> unavailable or inaccessible: Internal credentials cache error", since that
> looks like either psql.exe can't access the (inexisting) keytab file, or it
> can't access Window's Kerberos service.

psql wouldn't be accessing an actual keytab, it would be trying to
access a credential cache and it is failing on that, though if it was
just non-existant, I'd expect an error along those lines. Accessing the
Windows kerberos service would require either using SSPI, which psql can
be built to do, or using a bridge tool like KfW as mentioned above.

> Also, I see that psql.exe is trying to access a ccapiserver.exe which does
> not exist. Should psql.exe be able to access that ccapiserver.exe file? That
> means is the OSGeo4W QGIS installer, that also installs all things necessary
> for psql missing that ccapiserver.exe executable?

That's part of KfW and it's the Kerberos libraries, not directly psql,
that's trying to access it. If you want to get this working, probably
the next step would be to look into KfW.

> * has anybody ever succeeded in authenticating with psql.exe against Active
> Directory?

Yes, many times, thuogh more typically using SSPI support in psql
instead of GSSAPI and using TLS/SSL for encryption.

> * can you maybe tell me what's wrong from the error message above?
> * how can I proceed from here?

Either switch to using SSPI and TLS/SSL, or you could give KfW a try.
If you'd like encryption support with SSPI, that's a bit of a project.

> PS: Any way to make GSS more talkative? At this moment all that I can get as
> logs is the above "computer says no".

Well, you're hitting the same issue over and over, it looks like.
Usually it's more informative in the minor code.

Thanks,

Stephen