I'm not sure I follow. Are you saying, you want a user to log in and not go into a portal, but just a specific harness (to get rid of all the other links and whathaveyou) and open a specific work object? That should be doable. I would look at the activity which is called when that operator logs in. I'm not sure where you're getting the item ID. Is that being passed in as part of the request at log in?
It might be helpful to have a bit more context around the business requirement because there may be another technical approach that you could consider taking.
My business requirement is such that when a user logs in (for the first time ) the system should open a new Registration case for him . So he should see the first page of the Registration case which is a screenflow .
Which is the best way to do it ? We can use a portal and open our customized harness from it . We tried this approach but I was not able to create a new case and display it . We are able to see the harness with the header and footer but the case does open up . We were able to open a case with mashup code but we are trying to avoid all mashup and custom codes as per standards.