Invitation to new studies

If the participant is invited to participate in an additional study, they receive an email invitation with a specific registration link. The registration page has a link "Already registered? Log in" which redirects to the login page.
After logging in, participants are shown a modal with the text "You've been invited to join a new study", the name of the new study (but no description or logo), and buttons to "accept", "decline" or close the modal:
- Accept - completes the the registration for that participant to the new study
- Decline - rejects the invitation and no registration occurs
- Close - closes the modal, but the invitation stays valid until its expiry. If the participant re-logs into the participant portal, the modal re-appears
After being invited to a new study, if the participant logs in to the participant portal without checking their emails and clicking on the registration link the new study invite modal appears, as described above.