The participant has to register himself and create a password before entering the experience.  Your participants can be whitelisted* or not and, if you want, you can restrict the experience to only whitelisted participant.

You can also modify the password reset e-mail. With this option, you will be able to define a password reset e-mail as well. Participants will receive an email with a link to reset their password. You can write the subject and body of the email, and the “reset password” link will be automatically inserted at the end of the text you write.