This method is used for passwordless sign-ins where a OTP is sent to the user's email or phone number.
If the user doesn't exist, sign_in_with_otp() will signup the user instead. To restrict this behavior, you can set should_create_user in SignInWithPasswordlessCredentials.options to false.
If you're using an email, you can configure whether you want the user to receive a magiclink or a OTP.
If you're using phone, you can configure whether you want the user to receive a OTP.
The magic link's destination URL is determined by the SITE_URL.
Magic links and OTPs share the same implementation. To send users a one-time code instead of a magic link, modify the magic link email template to include \{\{ .Token \}\} instead of \{\{ .ConfirmationURL \}\}.