Function enroll 

async fn enroll(
    username: &str,
    sign_in_address: &str,
    sign_in_token: &str,
    context: &dyn SsoEnrollmentContext,
    rest: &RestClient,
    timing: &Timing,
    started: &mut Option<String>,
) -> Result<CredentialBundle, Stop>

The steps of the enrollment. The uuid goes to started as soon as the server hands it out, for the caller to cancel the enrollment should this be dropped halfway.