This is a new Key Distribution Center (KDC) option that MUST be set in a KRB_TGS_REQ message to request Service for User to Proxy (S4U2proxy) functionality. The kdc-options flags are specified in [RFC4120] section 5.4.1, and the new cname-in-addl-tkt option is defined as the KDC option with bit position 14.

 KDCOptions      ::= KerberosFlags
         -- cname-in-addl-tkt (14)