Validity for portal roles

Hi Experts,

Normally in SAP ABAP systems we can mention the validity for roles in user master data. In our client we have a Netweaver 7.3 system. We have developed some portal roles for user access. Some times we are requested to add a specific role for just 2 days. I can not see any validity from and validity to while adding roles to the users. Can you please help me how to maintain validity for roles in portal system.

Thanks in advance,

Regards,

Krish