Description of problem: 

Currently pam_cracklib/pam_pwquality does not have an option to specify the "minimum number of character in each class". We can specify the number of characters required for each class (by using -weight) however this is not sufficient in some situations, for example:

Requirement: 

Minimum length: 12
Minimum number of classes: 3
Minimum number of character in each class: 2

Cracklib/pwquality attempt is below:

password required pam_cracklib.so try_first_pass minclass=3 difok=4 retry=3 minlen=12 lcredit=-2 ucredit=-2 dcredit=-2 ocredit=-2

However, since -2 is specified for each class, pam is enforcing 4 classes. We cannot specify, the password only require 3 classes, but at least 2 characters for each class.