[PATCH] auth: Use AUTH_CACHE_KEY_USER instead of per-database constants

[PATCH] auth: Use AUTH_CACHE_KEY_USER instead of per-database constants

Fixes cache key issue where users would end up overwriting
each other in cache due to cache key being essentially static
string because we no longer support %u.

Forgotten in 2e298e7ee98b6df61cf85117f000290d60a473b8

Gbp-Pq: Name auth__Use_AUTH_CACHE_KEY_USER_instead_of_per-database.patch