Hi Damon,
Each employee will have his own unique ID so if you want to query LDAP using that ID then unfortunately you need to make these many calls. But the best way is to identify a group ID that all the user belongs to and query the LDAP to pull all users in that group with one call. Once you get a list of valid available users then you can write a logic to loop around your input users and details fetched from the LDAP query and then fetch the required details from logic for your individual user i.e. SAM Account name.
Hope this helps. Let us know if you find an alternate solution to this. Also, we wait for other users to respond to this like any short way to query LDAP with some user filter.
Regards
Firoz N
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