The critical essay to which you refer has been written by a member of the Enotes staff, so the only credit is that listed beneath the essay. You can locate this essay at this link:
Note that at the bottom of the essay, the credit is given to Enotes Publishing.
You may also wish to click on the link below which explains how to cite a URL in MLA style, which is what one uses for papers on literary works. MLA no longer requires URL addresses since that can change and people can usually locate the source via author or title of the essay, etc.
However, if the instructor demands the address, MLA suggests that you put the URL address in brackets after the access date. Here is how to arrange it:
"Irony in 'The Cask of Amontillado'" eNotes.com. eNotes.com, Inc.