UserIDs are not case sensitive in Windows because they have been forced to be upper case or normalized, so that if a UserID is x12345 that is the same as X12345. By default, Linux is case sensitive. If a userID of x12345 is sent to the PAM challenge in an include group, and the only entry is X12345, the userID will not match and therefore not be challenged.
If the PAM module had the option to normalize or force the case on Letters in a UserID, it would make the PAM agent similar to the Windows agent in regards to challenge group lookups.
