[subscription authentication] Who to extract cookie SID, compare with sessions in session store and set role in Postgres for the lifetime of the subscription?
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### Goal

Leverage the session with cookies to authenticate my users for subscriptions so that they have the correct role and user_id set to access the data they have GRANTs and RLS policy for in the Postgres database.

### Question

How to set a role in the database `SET ROLE authenticated;` according to user session data at the subscription time? 

### Additional context

I'm using cookies + [pgSettings function](https://www.graphile.org/postgraphile/usage-library/#pgsettings-function) + Passport.js + expressSession with Postgres database as session store.
