How do I add a reference to the System.IdentityModel.Tokens dll?
It does not seem to come up in the Nuget Package Manager.
Do I need to download the DLL?
I have .Net 4.5 installed.
The following code will not compile without the reference:
SessionSecurityToken sst = e.SessionToken;
It does exist on NuGet, and was last published 2013-02-08, so I don't understand why you couldn't find it. Try searching for System.IdentityModel.Tokens.ValidatingIssuerNameRegistry.
The best way is to install it is using the NuGet packet manager.
You can find the package here:
https://www.nuget.org/packages/System.IdentityModel.Tokens.ValidatingIssuerNameRegistry/4.5.0
In your solution, right click the References folder and choose "Add Reference"
From the Assemblies->Framework (.NET 4.5) list, select (check) System.IdentityModel
and the press ok.
Add the using statement to the top of your class - using System.IdentityModel.Tokens;
In case it helps someone else.
Depending on what class you need you may also need reference to
System.IdentityModel.Tokens.ValidatingIssuerNameRegistry.dll
This may not be obvious as it may be implicitly required by specific element in web.config file and not explicitly required in code.