Self Registration
Self Registration allows any users who come to your portal to log in using their Facebook, Twitter, or Google ID. To enable Self Registration, Customize the Support Portal.
In many cases, it makes sense to all users to register themselves. For example, if a product is sold through retail channels, customers will come to the service desk through the organization's website, and register to get support. In such circumstances, there is rarely a need to invite contacts to the Support Portal (although it can be done).
In other cases, access to the Support Portal is much more restricted. In a B2B setting, for example, only employees of a client company will be eligible to register as service desk users. In those circumstances, you'll want to Template:HDlink.