Re: [EXTERNAL] Re: [PoC] Federated Authn/z with OAUTHBEARER - Mailing list pgsql-hackers

On 9/21/22 21:55, Andrey Chudnovsky wrote:
> First, My message from corp email wasn't displayed in the thread,

I see it on the public archives [1]. Your client is choosing some pretty
confusing quoting tactics, though, which you may want to adjust. :D

I have what I'll call some "skeptical curiosity" here -- you don't need
to defend your use cases to me by any means, but I'd love to understand
more about them.

> Yes, passing a token as a new auth method won't make much sense in
> isolation. However:
> 1. Since OAUTHBEARER is supported in the ecosystem, passing a token as
> a way to authenticate with OAUTHBEARER is more consistent (IMO), then
> passing it as a password.

Agreed. It's probably not a very strong argument for the new mechanism,
though, especially if you're not using the most expensive code inside it.

> 2. Validation on the backend side doesn't depend on whether the token
> is obtained by libpq or transparently passed by the upstream client.

Sure.

> 3. Single OAUTH auth method on the server side for both scenarios,
> would allow both enterprise clients with their own Token acquisition
> and community clients using libpq flows to connect as the same PG
> users/roles.

Okay, this is a stronger argument. With that in mind, I want to revisit
your examples and maybe provide some counterproposals:

>> Libpq passing toked directly from an upstream client is useful in other scenarios:
>> 1. Enterprise clients, built with .Net / Java and using provider-specific authentication libraries, like MSAL for
AAD.Those can also support more advanced provider-specific token acquisition flows.
 

I can see that providing a token directly would help you work around
limitations in libpq's "standard" OAuth flows, whether we use iddawc or
not. And it's cheap in terms of implementation. But I have a feeling it
would fall apart rapidly with error cases, where the server is giving
libpq information via the OAUTHBEARER mechanism, but libpq can only
communicate to your wrapper through human-readable error messages on stderr.

This seems like clear motivation for client-side SASL plugins (which
were also discussed on Samay's proposal thread). That's a lot more
expensive to implement in libpq, but if it were hypothetically
available, wouldn't you rather your provider-specific code be able to
speak OAUTHBEARER directly with the server?

>> 2. Resource-tight (like IoT) clients. Those can be compiled without the optional libpq flag not including the iddawc
orother dependency.
 

I want to dig into this much more; resource-constrained systems are near
and dear to me. I can see two cases here:

Case 1: The device is an IoT client that wants to connect on its own
behalf. Why would you want to use OAuth in that case? And how would the
IoT device get its Bearer token to begin with? I'm much more used to
architectures that provision high-entropy secrets for this, whether
they're incredibly long passwords per device (in which case,
channel-bound SCRAM should be a fairly strong choice?) or client certs
(which can be better decentralized, but make for a lot of bookkeeping).

If the answer to that is, "we want an IoT client to be able to connect
using the same role as a person", then I think that illustrates a clear
need for SASL negotiation. That would let the IoT client choose
SCRAM-*-PLUS or EXTERNAL, and the person at the keyboard can choose
OAUTHBEARER. Then we have incredible flexibility, because you don't have
to engineer one mechanism to handle them all.

Case 2: The constrained device is being used as a jump point. So there's
an actual person at a keyboard, trying to get into a backend server
(maybe behind a firewall layer, etc.), and the middlebox is either not
web-connected or is incredibly tiny for some reason. That might be a
good use case for a copy-pasted Bearer token, but is there actual demand
for that use case? What motivation would you (or your end user) have for
choosing a fairly heavy, web-centric authentication method in such a
constrained environment?

Are there other resource-constrained use cases I've missed?

Thanks,
--Jacob

[1]
https://www.postgresql.org/message-id/MN0PR21MB31694BAC193ECE1807FD45358F4F9%40MN0PR21MB3169.namprd21.prod.outlook.com