Enable login to Portal via Email id

Hello Experts,

I am using SAP Portal 7.3 and its UME is configured to ABAP Data source,

I have a requirement where instead of logon id user will be using Email id to logon to Portal.

And need to ensure that SSO is not broken with the Backend system.

Any input or suggestions on how to configure it on Portal will be very helpful.

Thanks & Regards,

Siddharth