How to add external user to the group programmatically in SharePoint?

Question

Hi all,
I want add an external user to a sharepoint group:
When I run the below code in ConsoleApplication the user will be added to the DemoGroup,
but when I add my code to User Control and run the code on SharePoint it doesnt work and I get an error:
The user does not exist or is not unique.<nativehr>0x81020054</nativehr><nativestack></nativestack>
Now I change the code:
SPUser user = spWeb.EnsureUser(userName);
I get again an error:
The Specified user i:0#.f|IT2S|Doe, John was not found.
string extName = "Doe, John";
string domainName = System.Environment.UserDomainName;
// in sp this is way how we get the domain:
//string domainName = System.Environment.GetEnvironmentVariables()["USERDOMAIN"].ToString();
web.AllowUnsafeUpdates = true;
string userName = string.Format("i:0#.f|{0}|{1}", domainName, extName);
web.SiteUsers.Add(userName,"[email protected]", extName, "0222");
SPUser user = web.SiteUsers[userName];
if (user != null)
web.Groups["DemoGroup"].AddUser(user);
web.Update();
web.AllowUnsafeUpdates = false;
can anyone please help me and say why that not work? Or if someone have an idea?
thank you in advance
Ahmad
SP 2013 & SPD 2013 & VS 2013 & MSSQL 2012

Answer 1

Hi Linda Li,
yes I solve the issue with FBA:
http://chrisbarba.com/2013/07/16/sharepoint-2013-forms-based-authentication-fba/
and
http://sharepointsolutions.blogspot.de/2012/08/configuring-forms-based-authentication.html
with above links I solved the task.
Best Regards
Ahmad
SP 2013 & SPD 2013 & VS 2013 & MSSQL 2012