Has anyone figured out how to cache Users when using Ldap to authenticate?

Create a structure with loginname and time, check this when the user goping trough the AREAVerifyLoginCallback. If the user is there, drop out and send the OK code and update the time settings. If not continue autenticate, after the user are OK add the user to the structure list. In the AREANeedToSyncCallback add some kind of code to check if the time (loginname) is older than x seconds, then free this user from the structure list.

can you please let me know how to cache the user in the AREA plugin for External Authentication