Add FBA Roles to SharePoint 2013 site and assign permissions programatically

I have a problem with adding a FBA role to a sharepoint 2013 site programatically. I tried web.ensureuser method and web.Siteusers.Add() methods and none of them works for me.

SPUser spUser = spWeb.EnsureUser("c:0-.f|ie-fbarolesprovider|groupName");

Thanks

shharepoint developer