Sunday, March 15, 2020

Authenticate PostgreSQL users against the Amazon AWS Cognito service

I was asked recently if PostgreSQL could authenticate login users against AWS Cognito.  Since PostgreSQL allows PAM authentication, I was pretty sure it could.

But an (admittedly not exhaustive) search on the web did not produce any PAMs for Cognito.

So I wrote one, using pam-pythonboto3, warrant and pyJWT:

It is designed primarily for PostgreSQL and pgbouncer, so it only supports pam_sm_authenticate and pam_sm_acct_mgmt, and all the work is done in pam_sm_authenticate. Because calling Cognito is comparatively slow, I didn't want to call it twice.

The necessary pam.d config is:

# Information for PostgreSQL process with the 'pam' option.
auth required aws_region user_pool_id client_id 
account required

If you use PAM authentication, passwords are sent in cleartext, so transport layer encryption, e.g. SSL/TLS, between client and server becomes mandatory!

I think it does the correct dance of authentication with Cognito and supports USER_SRP_AUTH, but if you see any problem, please raise a paw.

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