In Drupal Commerce how do you auto login an anonymous user that has completed checkout? I have Drupal 7 Commerce core installed and configured manually. Not kickstart.

Currently after completing a Commerce checkout (Paypal Express) with an anonymous user, I get redirected back to the "Checkout Complete" page. The page gives a link to Review My Order, but it asks for login details which I do not have since it was an anonymous checkout. 

Is there a way to auto login the user after the Successful Checkout?
In short summary to the link Clive posted in case if it ever gets deleted on the interwebs:

http://s1l.org/automatic-user-login-anonymous-checkout

Step 1 - Make sure Anonymous checkout is checked on. (Permissions > Access Checkout)

Step 2 - Make sure Commerce Immediate Login module is enabled: http://drupal.org/sandbox/simongeorges/1676742

Step 3 - Add a User Login Action to the default Commerce "Create new account for anonymous order" Rule (Configuration -> Workflow ->Rules)

--- rules/reaction/manage/Create a new account for an anonymous order

Step 4 - Click Add action > Login User (under system) > type "account-created" > SAVE

Step 5 - TEST!