Redirecting mydomain.com to www.mydomain.com

I'm setting a web server running Windows 2012.  Currently, if the user types in either mydomain.com orwww.mydomain.com in the browser, they resolve just fine.  But, IIS is apparently treating them separate as my session variables aren't working between the two "sites".  No real surprise there. 

I currently have the bindings defined like this:

http    www.mydomain.com    80
https   www.mydomain.com    443
http    mydomain.com        80
https   mydomain.com        443

So, my question is, how can I get get IIS to automatically redirect/resolve/whatever-it-is-called any browser requests for mydomain.com towww.mydomain.com?  Which would solve any issues/complications of having "two" sites.

Thanks,

Richard