We have a scenario where we need to display case feed items to users in the customer portal. We are using Chatter API to get the details. It works fine when the logged in user has created the case or is a contact on the case.

However for the scenario, where a user wants to see other cases e.g. all cases at an account level it fails as chatter api uses the logged in user context and the user does not have access to the case. We would want to change the context of the user to another user (who would be having access to all cases and would be used only at an API call level).

Is that possible?

We have a portal and planning for a migration to communities. We would want to start with something basic and do a phased migration. Would like to know if portals and communities can co-exist??