SAP Web Dispatcher is capable of forwarding the client X.509 certificate to the AS JAVA using header variables. If you are terminating SSL on the WD, you will have to set a instance profile parameter so HTTP can be used to forward the certificate although it is not the recommended approach. See the attached link for details.
http://help.sap.com/saphelp_nw73ehp1/helpdata/en/48/9ab5d73e6d062be10000000a42189d/frameset.htm