Function join 

pub(crate) fn join(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    place: String,
    passphrase: String,
    again: String,
)

Joins the sharing through place on the server signed in to, with the passphrase (typed once, checked against the folder’s seal; twice, again, for a new sharing there), off the window’s thread; then a first exchange at once, the contacts and calendars of that server, and what came, said. The grant is kept while the passphrase is wrong, for another try.