“Middleware” is a term for the type of software that is used to read your CAC because it has no use on its own but instead sits in the middle of two other things — your CAC and the site you are attempting to access.
ActivClient is the CAC middleware that is in use by the DoD. You need this software in order to access AKO/DKO using your CAC. This software comes automatically on any GFE computer and you will not need to obtain it for normal operations. If you wish to log in to AKO or other sites using your CAC from a COTS/personal home system you will need to obtain this software.
If you are in the Army, Army National Guard, Army Reserves, or are a Department of the Army Civilian you can download this software right off of AKO at our ActivClient page located at: https://www.us.army.mil/suite/page/610885
If you have any questions or issues please see our FAQ for ActivClient inside the portal at: https://www.us.army.mil/suite/page/614851
For all other service branches you should be able to obtain ActivClient through your local network operations support. For details on this please visit http://www.militarycac.com