You might want to constrain users in a collaboration to a particular set of applications.
In the SRAM portal, you can create a group "src_no_ext_apps" inside the collaboration.
Any user that is added to this group will only be able to use applications that have been explicitly allowed for this collaboration.
The more generic, "public" applications will not be available, for this user, inside this collaboration.
Of course, if the user is a member of another collaboration, they will be able to use public applications through the other collaboration.