HI Mustafa and Jebeni
You should not need to create end users in GRC because of Portal Integration. It defeats the purpose of the GRACUSER concept and may impact your product licensing arrangements with SAP
If you have your data source for authentication pointing to the portal source, possible your can look at SSO to avoid need for password.
1733439 - How to auto forward to GRC Application after login into Portal using SSO
1733442 - Approaches to set SSO using Active Directory in AC 10.0
For your solution - what is the UME for Portal - is it the ERP system, AD or Portal? This may impact how you do your solution. End User Login is the functionality to avoid creating SU01 records in GRC for all users.