In the Global Settings, you'll see a small but important setting titled 'Allow registrations' with an option to select either "Yes' or 'No'.
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Selecting 'Yes' means that Twine becomes an open system: anybody can register an account for your system.
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Selecting 'No' means that Twine becomes a closed system: users will need an invitation or to sign in using third party service (covered in the authorisation section of the Help Centre).
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To keep your system secure, it's important you select the correct option. By default, Twine is set to be a closed system.
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