SASL SCRAM Support

[jwp]

https://www.postgresql.org/docs/current/auth-password.html
https://www.postgresql.org/docs/current/sasl-authentication.html

https://github.com/postgres/postgres/blob/master/src/include/common/scram-common.h
https://github.com/postgres/postgres/blob/master/src/include/libpq/scram.h
https://github.com/postgres/postgres/blob/master/src/common/scram-common.c
https://github.com/postgres/postgres/blob/master/src/interfaces/libpq/fe-auth-scram.c
https://github.com/postgres/postgres/blob/master/src/backend/libpq/auth-scram.c

[ensslen]

This is a really cryptic ticket (pun intended). For anyone who doesn't already know, this ticket would fix the following error: postgresql.exceptions.AuthenticationMethodError: unsupported authentication request '<unknown>'(10) which causes postgresql.exceptions.ConnectionRejectionError: Connection refused. My stackoverflow question may prove helpful for work arounds: https://stackoverflow.com/q/69488696/7359502

[rokclimb15]

@jwp do you have any WIP on this? I'm potentially interested in taking on the work to deliver this feature.

[jwp]

I do not. Only collected a few links of context to save myself some time in the case that I felt inspired to work on it, but that has yet to happen.

From what I recall reading, PG's SASL usage is rather specialized and shouldn't require a framework of any sort. If you do work on this, avoiding dependencies would be preferable. (Not that I think they're bad, but git clone and go is probably worth preserving for most/all patches)