There are a number of articles on the subject. One article can be found here. I found helpful the quote in the article from the Lutheran theologian, John W. Montgomery, who sums up Luther's criteria:
In his Preface to Jude we heard Luther say: “Although I value this
book, it is an Epistle that need not be counted among the chief books
which are to lay the foundations of faith”; why? “The ancient fathers
excluded this Epistle from the main body of the Scriptures.” Again
and again in his Prefaces we find Luther arguing in this vein: “Up to
this point we have had to do with the true and certain chief books of
the New Testament. The four which follow have from ancient times had a
different reputation.” “This Epistle of St. James was rejected by the
ancients.” “Many of the fathers also rejected this book [Revelation:
Luther’s Preface of 1522] a long time ago.” Here Luther appeals not to
subjective considerations but objectively to the judgments of the
early church, specifically to what Jerome says in his De viris
illustribus, chap. 2, and to what Eusebius reports in his
Ecclesiastical History, Bk. II, chap. 23 and Bk. III, chap. 25. The
negative evaluations of antilegomena by certain church fathers were
certainly unjustified, as history proved, but Luther had every right
to raise the question in terms of the fathers. Unless one is going to
make the fatal error of accepting the content of Scripture because the
institutional church has declared it such,… there is no choice but to
refer canonicity questions to the earliest judgments available
historically concerning the apostolic authority of New Testament
books. Christ promised to the apostolic company a unique and entirely
reliable knowledge of His teachings through the special guidance of
His Holy Spirit (John 14:26), so the issue of the apostolicity of New
Testament writings has always been vital for the church. As a
theologian, Luther had the right, even the responsibility, to raise
this issue, and did not become a subjectivist by doing so.”
