The EDA accesses only one application at a time. The operating system does not function like Windows in which you can have multiple sessions open at the same time. With the EDA you must exit one application to access another.
When you login to one application, you remain logged in until you either clear your login information or you login to another application.
For PrismCore, you can use your regular login and password or your store may have a specific login established for use with the EDA.