You can click on the Google or Yahoo buttons to sign-in with these identity providers,
or you just type your identity uri and click on the little login button.
The identifier attribute should be unique.
How is this related to ticket #3299729?
The questionnaire is not subject dependent and thus it may have an identifier.
The ticket #3299729 is a more global refactoring/cleanup of identifiers logic.
Ticket #3299986 - latest update on 2014/01/20, created on 2013/11/15 by Vincent Michel