Gdn_Authenticator::setIdentity PHP Method

    public function setIdentity($UserID, $Persist = true)
    {
        $AuthenticationSchemeAlias = $this->getAuthenticationSchemeAlias();
        Gdn::authenticator()->setIdentity($UserID, $Persist);
        Gdn::session()->start();
        if ($UserID > 0) {
            Gdn::session()->setPreference('Authenticator', $AuthenticationSchemeAlias);
        } else {
            Gdn::session()->setPreference('Authenticator', '');
        }
    }