To limit who can and cannot log in to your system using third party services (e.g. Google, LinkedIn), you'll need to manage which domains the system should allow.
If you want to let anybody join the system (perhaps you are using Twine as an extranet or a public facing portal), you might want to let anybody join. That's fine, you can use an asterisk (*) to enable login from any domain.
If you want to limit who can join, you configure the system so that it only allows logins from certain domains . For example, if your company's website was 'www.bobs-tomatoes.com' you might only allow email addresses that use the domain 'bobs-tomatoes.com'.
To do this, go to Settings > Authentication > Domains
Next, press Add new domain. Now type in the domain that you wish to authorise and press Save.
You can add as many domains as you wish – just repeat this process for each one.