It appears that U.S. and Iran will be working together to combat the Afghan drug trade.

This is basic common sense. Diplomacy can be based on common values or common interests, and there is a common interest here: The Shias in Iran, and the Sunni Taliban hate each other, the Taliban going so far as to murder Iranian diplomats, and Iran as a huge drug problem, with supplies from Afghanistan at its root.

There is a common interest here, and it can be the basis of joint action.