This question about Authentication or Authorisation: Answered
Ldap cache seems to not allow certain logins
I have foswiki 1.1.18 setup to use LdapContrib with precache enabled - this appeared to cause an issue whereby someone couldn't authenticate via ldap yet I could. I turned off the precache and then was able to successfully login as both people.
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CarlEastman - 06 Aug 2013
Can't say what's going on without further details. Try
%LDAPUSER{hideunknown="off"}%
to render a list of all users being pre-cached. The two user records might not be in the list. So the issue might be that
LdapContrib wasn't able to read both records from the same branch or that there are other properties of the record that prevents it from being added to the pre-cache.
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MichaelDaum - 04 Jul 2014