Re: Amazon RDS auth tokens in .pgpass

Nicholas Chammas <nicholas(dot)chammas(at)gmail(dot)com> writes:
> I am trying to connect to a Postgres database on Amazon RDS using IAM
> authentication. This works by having IAM generate an authentication token
> that you use as the password for the database user you're connecting as.
> You can read more about this here:
> https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/UsingWithRDS.IAMDBAuth.Connecting.AWSCLI.PostgreSQL.html
> Here's an example of what one of these auth tokens looks like (with some of
> the sections redacted/altered from a real token):

> ```
> some-host.us-east-1.rds.amazonaws.com:5432/?DBUser=someuser&Action=connect&X-Amz-SignedHeaders=host&X-Amz-Security-Token=FwoGZXIvYXdzEHcaDD1hC2q3GGNNaftOvCLRAetaDArXOt6kpr1Ac83hzwtPxEojvZzARJN%2Ftys%2BkLnxsP6FmHmIMmMERWeGBiJmNcUyXWYY%2BSU9oduSSeAv%2BCpYy028Cep%2Bpyl1Km3B5axPAA2q0L4NWa41LQOayWF8F7%2FlB540%2B0aSkZ%2BIucM%2BLZXTcQl3Q0nJiIgu65lhuME4q3Mvst1ZEaZWfUegCWGaX0npajiKbNU2Ut3FH%2F6046RxlNwO4jg4vteTcPk%2BfgMjuAkf5gFR9EYMTziRx1dJGJn8VGFLTugGVITQI%2FEC1iuqKNb%2Fs%2FoFMisfzgF1nd7kxcZYYAmQtugBnDuJuIboYwYAXI2qn7HDbhgQ5v%2FwPWfZieWO&X-Amz-Credential=ABCDEFGHIJKLMNOPQRST%2F20200831%2Fus-east-1%2Frds-db%2Faws4_request&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Expires=900&X-Amz-Date=20200831T163708Z&X-Amz-Signature=fb41c59dcaf4e013eda6885a4d456549366d2612ecf06307d2443b6a44461ab7
> ```

Ugh :-(

> It's only the combination of a) .pgpass and b) RDS auth token that doesn't
> work. This leads me to believe something is going wrong on a code path
> specific to .pgpass, or that there are some undocumented restrictions on
> what can go in .pgpass.

Looking at the source code, there's a hard-wired restriction that lines of
.pgpass can't be more than 320 characters long (well, NAMEDATALEN*5, but
very few builds don't have NAMEDATALEN=64). I see that somebody very
recently added code to make libpq print a warning for overlength lines,
but I wonder why they didn't just, um, remove the restriction. We had
not previously heard of a use-case for passwords with hundreds of
characters in them, but I guess we need to cope.

If you're in a position to rebuild libpq, could you check that changing
LINELEN in fe-connect.c to something large enough (like 1K) fixes your
problem? While that's clearly one issue, it'd be good to verify that
there's not another one lurking behind it.

regards, tom lane