Cache LDAP UserDN searches

Description

When querying for users from LDAP, there are a lot of duplicate search queries being made.

One way to improve performance is to cache search results, which is the topic of this issue: userDN search results can be cached.

Note that this might not be the best way, or even a safe way, to improve performance. This needs further review.

Environment

None
Fixed

Assignee

Dave Cridland

Reporter

Guus der Kinderen