Function begin_signed_in 

pub fn begin_signed_in(
    memory: &Path,
    folder: &Path,
    login: &Login,
    opened: &Opened,
    now: i64,
) -> Result<(), String>

The same, joined through the server’s own sign-in (loginflow): the folder kept with that login (State::user), its app password from the keyring under that login, whatever account the contacts and calendars use; login.account names the account of this server and login, made or found here.