Hello Mohammad,
Using SAP SSO will allow you to implement this scenario. In addition you will have the options to enable multi-factor authentication for external access and SSO for mobile devices. The AS Java system where SAP SSO is deployed has to be exposed to Internet as well but it is not 'between' the Web Dispatcher and the GW server. It is behind the Web Dispatcher and next to the GW server. A similar setup is shown in scenario 3 of the following blog: http://scn.sap.com/community/sso/blog/2015/05/22/stronger-security-for-your-business-data-at-risk, where SAP Web Dispatcher = Reverse Proxy, SAP SSO = Portal / IDP, Gateway = ERP
Regards,
Dimitar
Additional resources:
