Re: No psql md5 auth, psql 14.1 to PG 11

Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
> On 4/18/22 13:12, Pete O'Such wrote:
>> I'm unable to authenticate with psql to a PG 11 database on server A
>> from server B which has PG 14.1 installed.  So it's psql 14.1 not
>> authenticating to PG 11.  Other clients can and do authenticate to the
>> PG 11 database, it only seems to fail with the psql 14.1 client.
>>
>> The PG 11 server uses md5.  So is the PG 14.1, but I didn't expect that
>> to matter for a straight psql connection plus interactive password entry.

> My first thought was that is was a md5/scram-sha-256 issue but I'm not
> sure how as both versions support both password types.

I just checked the case here, and I can connect fine from psql 14 to
a v11 server with a password stored in md5. So I'm not sure what's
up either, but there has to be something off-the-beaten-path about
this.

Looking at the v14 code, the error message tells us that
pg_password_sendauth failed, which has several possible explanations:

* pqGetnchar failed, which'd imply a malformed server challenge message.
Seems unlikely, if other clients can connect.

* pg_md5_encrypt failed. Hard to believe ... unless the v14 psql
is running on a FIPS-mode machine, which'd refuse all MD5 operations?

* pqPacketSend failed, ie server disconnected after sending the
challenge. Also seems doubtful.

So my recommendation is to check for FIPS mode.
If it's a recent Linux, what does "sysctl crypto.fips_enabled" say?
(This theory also requires that v14 was built with openssl support.)

FWIW, v15 will provide a more on-point error message in such cases.

regards, tom lane