Anton Chu wrote:

Unfortunately there's can only be one GID number per user entry into the DIT, how can I assign multiple groups to one user? So when that user logs into a server, he or she will have multiple group IDs.

That GID is their PRIMARY GID. You can then add them to multiple SECONDARY groups by creating a posixGroup and add them to it:

dn: cn=tstgroup,ou=Group,dc=example,dc=com objectClass: posixGroup objectClass: top cn: tstgroup memberUid: alice memberUid: bob memberUid: marilena memberUid: charlie gidNumber: 501