More flexible portal-specific customer signup

Problem Definition

Currently, when a user signs up for Service Desk using a specific Customer Portal URL, he is automatically added to and can begin to raise issues on any Service Desk that has customer signup enabled (i.e. all projects that have request security set to "Anyone can sign up for a customer account on my Customer Portal"). This makes it hard to configure Service Desk for scenarios where specific customers should only be able to signup and raise requests on specific portals only, while there are other portals on the same instance that will allow signup for other specific group of customers only.

The main problem here seems to be the fact that all Service Desk projects are required to have the Service Desk Customer - Portal Access granted basic permissions by default e.g. Create Issue, Browse projects etc (https://jira.atlassian.com/browse/JSD-3421). This makes it hard to restrict these project permissions, except of course by entirely disabling customer self-signups by using request security option: 'Only people on my customers list can raise a request').

Solution

Make request security and public signup more flexible for Service Desk admins who want to allow anyone with a portal URL to be able to signup, but then to only be able to raise issues on the specific portal on which they signed up on, and no other.