Cannot Access Torghast

Once you have reached level 60 and have pledged yourself to a Covenant, you will be offered a questline which will take you to The Maw. From there you wil eventually receive the quest Into Torghast which unlocks Torghast itself.

Once you have completed the questline, a portal to Torghast will become available at the back portion of Ve'nari Refuge in The Maw. There are no requirements to enter Torghast beyond completing the questline. Torghast itself is not limited by keys and there is no item that you have to buy to get in.