Shared hosting with FDW on AWS RDS

Hi,

We'd like to configure an RDS server for shared hosting. The idea is that every customer will be using a different database and FDW will be configured, so that the remote tables have access to the full data, but materialized views will be pulling from them data specific to each customer. So far, everything seems to work fine and be secure, as we've revoked access to the remote tables for the customer users, but I'm feeling a bit uneasy considering that the credentials for full access are stored in each database. My understanding is that remote user mapping is designed so that this will not be an issue, but I was wondering if access to the metadata schema might allow to circumvent this restriction. Also, I was wondering if someone has experience hardening databases on RDS, as the so called superuser does not have the right to revoke access from the metadata schema.

Comments and suggestions are welcome.
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Regards,
Peter