If a pseudonym is listed on the work, you may refer to the author in your prose by the pseudonym:

The title page of the 1575 printing of Gammer Gurton’s Needle, one of the earliest surviving comedies in English, gives its author as Mr. S, Master of Art.

At the first mention of the work in your prose, add a note that names the authors the work has been attributed to. If the authorship is relevant to your discussion of the work, you will probably want to provide more details as well as references to sources about the authorship. If the work’s authorship is not central to your discussion, simply acknowledge that authorship is uncertain and list the possible authors.

Your works-cited-list entry may treat the work as anonymous (as most modern editions of this play do):

Gammer Gurton’s Needle. 1575. HathiTrust Digital Library, babel.hathitrust.org/cgi/pt?id=njp.32101071988586;view=1up;seq=7.

Or you may use the pseudonym in your works-cited-list entry:

Mr. S, Master of Art. Gammer Gurton’s Needle. 1575. HathiTrust Digital Library, babel.hathitrust.org/cgi/pt?id=njp.32101071988586;view=1up;seq=7.

If the work has been attributed to only one author but authorship is yet uncertain, you can indicate the attributed author in your works-cited list in square brackets and with a question mark:

Mr. S, Master of Art [John Still?]. Gammer Gurton’s Needle. 1575. HathiTrust Digital Library, babel.hathitrust.org/cgi/pt?id=njp.32101071988586;view=1up;seq=7.