Get multisite "admin_url" into redirect.

I’m setting up ajax login from home page and redirect to “site.com/username/wp-admin” but cannot get the url right.

function ajax_login_init() {

      global $mk_options;

      $theme_js_hook = ($mk_options['minify-js'] == 'true') ? 'theme-scripts-min' : 'theme-scripts';

      wp_localize_script( $theme_js_hook, 'ajax_login_object', array(
                  'ajaxurl' => admin_url( 'admin-ajax.php' ),
                  'redirecturl' => site_url(),
                  'loadingmessage' => __( 'Sending user info, please wait...' , 'mk_framework')
            ) );

}
if ( !is_user_logged_in() ) {
      add_action( 'wp_footer', 'ajax_login_init' );
}

add_action( 'wp_ajax_nopriv_ajaxlogin', 'ajax_login' );

Only thing that matters is ” ‘redirecturl’ => site_url(),” and i need to replace the “site_url()” with “http://site.com/username/wp-admin/” but everything I try does not work.

I think what I need is something like this
'redirecturl' => 'http://site.com/' . $current_user->user_login . '/wp-admin',
But this does not work, as it cannot detect username, and redirects to http://site.com/wp-admin