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

On Wed, 2021-08-25 at 15:25 -0700, Zhihong Yu wrote:
> 
> Hi,
> For v2-0001-common-jsonapi-support-FRONTEND-clients.patch :
> 
> +   /* Clean up. */
> +   termJsonLexContext(&lex); 
> 
> At the end of termJsonLexContext(), empty is copied to lex. For stack
> based JsonLexContext, the copy seems unnecessary.
> Maybe introduce a boolean parameter for termJsonLexContext() to
> signal that the copy can be omitted ?

Do you mean heap-based? i.e. destroyJsonLexContext() does an
unnecessary copy before free? Yeah, in that case it's not super useful,
but I think I'd want some evidence that the performance hit matters
before optimizing it.

Are there any other internal APIs that take a boolean parameter like
that? If not, I think we'd probably just want to remove the copy
entirely if it's a problem.

> +#ifdef FRONTEND
> +       /* make sure initialization succeeded */
> +       if (lex->strval == NULL)
> +           return JSON_OUT_OF_MEMORY;
> 
> Should PQExpBufferBroken(lex->strval) be used for the check ?

It should be okay to continue if the strval is broken but non-NULL,
since it's about to be reset. That has the fringe benefit of allowing
the function to go as far as possible without failing, though that's
probably a pretty weak justification.

In practice, do you think that the probability of success is low enough
that we should just short-circuit and be done with it?

On Wed, 2021-08-25 at 16:24 -0700, Zhihong Yu wrote:
> 
> For v2-0002-libpq-add-OAUTHBEARER-SASL-mechanism.patch :
> 
> +   i_init_session(&session);
> +
> +   if (!conn->oauth_client_id)
> +   {
> +       /* We can't talk to a server without a client identifier. */
> +       appendPQExpBufferStr(&conn->errorMessage,
> +                            libpq_gettext("no oauth_client_id is set for the connection"));
> +       goto cleanup;
> 
> Can conn->oauth_client_id check be performed ahead
> of i_init_session() ? That way, ```goto cleanup``` can be replaced
> with return.

Yeah, I think that makes sense. FYI, this is probably one of the
functions that will be rewritten completely once iddawc is removed.

> +       if (!error_code || (strcmp(error_code, "authorization_pending")
> +                           && strcmp(error_code, "slow_down")))
> 
> What if, in the future, there is error code different from the above
> two which doesn't represent "OAuth token retrieval failed" scenario ?

We'd have to update our code; that would be a breaking change to the
Device Authorization spec. Here's what it says today [1]:

   The "authorization_pending" and "slow_down" error codes define
   particularly unique behavior, as they indicate that the OAuth client
   should continue to poll the token endpoint by repeating the token
   request (implementing the precise behavior defined above).  If the
   client receives an error response with any other error code, it MUST
   stop polling and SHOULD react accordingly, for example, by displaying
   an error to the user.

> For client_initial_response(),
> 
> +   token_buf = createPQExpBuffer();
> +   if (!token_buf)
> +       goto cleanup;
> 
> If token_buf is NULL, there doesn't seem to be anything to free. We
> can return directly.

That's true today, but implementations have a habit of changing. I
personally prefer not to introduce too many exit points from a function
that's already using goto. In my experience, that makes future
maintenance harder.

Thanks for the reviews! Have you been able to give the patchset a try
with an OAuth deployment?

--Jacob

[1] https://datatracker.ietf.org/doc/html/rfc8628#section-3.5