Having public visibility gives all users the ability to create accounts regardless of domain. This also enables spam accounts to be created.
Adding specific domains such as @gmail.com or @hotmail.com enables users with those domains to create accounts and get access to the portal. This prevents spam accounts.
There are 2 ways to add SPECIFIC users for this portal. Either individually add the members or a batch upload, adding multiple at once. Using this option enables the specific emails to create users on the portal. If uploading a file for batch loading, the file must be in a ".txt" format and either have one email per line or use commas to separate emails. After adding members to the email list, that email address is now enabled to create an account on the portal to view more. No email is sent to the email address until after manually creating the account.
This is going through a custom login that is already created for your site, the registering and logging in can be done through your pre-made login screen.
Similar to OAuth2 but gives enables certificates to be given from the portal to the users computer.