This is similar to b69aba7, except that this completes the work for
HMAC with a new routine called pg_hmac_error() that would provide more
context about the type of error that happened during a HMAC computation:
- The fallback HMAC implementation in hmac.c relies on cryptohashes, so
in some code paths it is necessary to return back the error generated by
cryptohashes.
- For the OpenSSL implementation (hmac_openssl.c), the logic is very
similar to cryptohash_openssl.c, where the error context comes from
OpenSSL if one of its internal routines failed, with different error
codes if something internal to hmac_openssl.c failed or was incorrect.
Any in-core code paths that use the centralized HMAC interface are
related to SCRAM, for errors that are unlikely going to happen, with
only SHA-256. It would be possible to see errors when computing some
HMACs with MD5 for example and OpenSSL FIPS enabled, and this commit
would help in reporting the correct errors but nothing in core uses
that. So, at the end, no backpatch to v14 is done, at least for now.
Errors in SCRAM related to the computation of the server key, stored
key, etc. need to pass down the potential error context string across
more layers of their respective call stacks for the frontend and the
backend, so each surrounding routine is adapted for this purpose.
Reviewed-by: Sergey Shinderuk
Discussion: https://postgr.es/m/Yd0N9tSAIIkFd+qi@paquier.xyz
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