Feature Request: Add AES-128-CFB Mode Support to pgcrypto

Dear PostgreSQL Development Team,

I would like to request the addition of support for the *AES-128-CFB* mode
in the pgcrypto extension. Currently, pgcrypto supports AES encryption
modes like ECB and CBC, but it does not include CFB mode, which is
essential for certain use cases.

In managed environments such as *Azure Database for PostgreSQL - Flexible
Server*, users are unable to create or install custom extensions. This
restriction makes it challenging to work with encrypted data that relies on
AES-128-CFB, as we cannot use custom solutions to handle this algorithm.
Adding CFB mode support to pgcrypto would address this limitation and
expand its usability in managed PostgreSQL environments.

Implementing AES-128-CFB in pgcrypto should require only minimal changes,
as it is already built on OpenSSL, which supports the CFB mode natively.
Including this functionality would also align pgcrypto with the principle
of providing robust cryptographic support, similar to other database
solutions.
Why This Matters:

1. *Compatibility*: Many existing systems encrypt data using
AES-128-CFB, and without native support in pgcrypto, PostgreSQL users
must resort to inefficient workarounds.
2. *Consistency*: pgcrypto already supports other AES modes (e.g., ECB,
CBC). Including CFB would ensure that its AES capabilities are complete.
3. *Ease of Implementation*: OpenSSL already provides a straightforward
API for AES-128-CFB, so adding it to pgcrypto should require only a few
lines of code.

This enhancement would greatly benefit users in managed environments and
improve the flexibility of PostgreSQL as a whole.

Thank you for considering this request. I would be happy to assist in
testing or providing further information if needed.

Best regards,
Vladyslav Nebozhyn