Ekansh,
I was testing exactly like you suggested. With debugger, using rest client with the extension ?sap-ds-debug=true. It stopped at the methods. Sy-uname was always user1. I thought may be because I am logged in with user1 id. So removed debugger and wanted to see order changes using update method(PUT). Order changes always show user1 id. I tested this with Basic(backend) + HTTP (SMP).
I could not test SSO, because MYSAPSSO2 cookie is not set properly and I do not know how to do.
In my case, GW is installed in the same SAP system.
Pls let me know where else I could have over looked.
Thanks
seenu