How to find the Microsoft.SharePoint.Identitymodel.dll location in SharePoint-2013 development environment?

I was searching on "session timeout and setup sliding sessions on an FBA enabled site". Where i need to add a reference namespace "Microsoft.SharePoint.IdentityModel". I have spend lot of time searching it and trying to add it in solution.

Please follow below steps to get the dll.

1. Open the Windows Explorer

2. Navigate to C:\Windows\Microsoft.NET\assembly\GAC_MSIL\ Microsoft.SharePoint.IdentityModel

3. And you can find the dll here C:\Windows\Microsoft.NET\assembly\GAC_MSIL\ Microsoft.SharePoint.IdentityModel\v4.0_15.0.0.0__71e9bce111e9429c


But it's not so simple some time as GAC_MSIL folder is not visible (Missing) in the assembly folder.

Here are few ways you can get it :

A)

1. start > run > cmd
2. type : "cd\windows\assembly"
3. type: "attrib -r -h -s desktop.ini"
4. type: "ren desktop.ini desktop.bak"

now open the GAC folder normally in your explorer. 
B)

1. Run regsvr32 /u C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\shfusion.dll
2. shfusion.dll is an explorer extension DLL that gives a distinct look to the GAC folder. Unregistering this file will remove the assembly cache viewer and the GAC folder will be then visible as any normal folder in explorer.
3. Open “%windir%\assembly\GAC_MSIL”.

Hope it helps you too.