The property sheet CredentialRequest was used to override birthday property from Person property sheet.
Because Person.birthday stores its value in start_date attribute.

Because property surcharge behaviour is not predictable (Which accesor will be took ?), CrendentialRequest now introduce date_of_birth property.
It avoid collision with start_date property which is also defined on Tickets.

All dialog action keeps birthday as input parameter to not break backward compatibility
my_date_of_birth_field is able to display getBirthday value to not break UI for ancient documents.