To use Double-Opt-In, a redis version greater or equal to 3.0 has to be installed.
Double-Opt-In on the applicant portal can be activated by checking
Administration → Miscellaneous → Applicant portal settings → {Your ApplicantPortal} → General settings → Double-Opt-In registration.
Afterwards, Double-Opt-In should be activated for registration on the portal and is used as follows:
1.) An applicant creates a new profile in the applicant portal
2.) This applicant data is saved for 24 hours in the redis database
3.) After successful pre-registration, a double-opt-in token is generated by the API and sent to the applicant via e-mail.
4.) Through the Double-Opt-In link and the token, the applicant is forwarded to the registration page, where is his name and email have already been filled out. Afterwards, the registration process takes place as usual.