search uid

http://www.cisco.com/en/US/docs/security/nac/appliance/configuration_guide/412/cas/s_adsso.html#wp1155714

Step 9 Search Filter—The attribute to be authenticated. The search attribute to be matched with any user in the base of the LDAP tree. For example:

•CN=$user$, or

•uid=$user$, or

•sAMAccountName=$user$