By default, the Packaged Apps are installed using the Application Express Accounts authentication scheme. For more details on that specific authentication scheme, I recommend taking a look at section 184.108.40.206 Application Express Accounts of the User's Guide. This type of authentication is based upon the workspace users. So much like your own account, to log into your workspace, the users you wish to have access to the app in question must exist as users in your workspace. For specifics on creating users, take a look at Managing Users in a Workspace in the Admin Guide.
I hope this helps.