What is this "divine authority" that you believe God gave to John?
I believe John was called and ordained by Jesus Christ to be an Apostle, which is a witness for Christ. This calling and ordination gave John certain authority. This does not make him infallible or an object of worship. He's just a person. However, he was chosen by God to have the great revelation on the isle of Patmos for the benefit of the world. The Book of Mormon, which I also believe, says this about John the Revelator. This is a revelation which I believe was given to a Book of Mormon prophet about 600 years before Christ (and John):
" 23 Wherefore, the things which he shall write are just and true; and behold they are written in the
book which thou beheld proceeding out of the mouth of the Jew; and at the time they proceeded out of the mouth of the Jew, or, at the time the book proceeded out of the mouth of the Jew, the things which were written were plain and pure, and most
precious and easy to the understanding of all men.
24 And behold, the things which this
apostle of the Lamb shall write are many things which thou hast seen; and behold, the remainder shalt thou see.
25 But the things which thou shalt see hereafter thou shalt not write; for the Lord God hath ordained the apostle of the Lamb of God that he should
write them.
26 And also others who have been, to them hath he shown all things, and they have
written them; and they are
sealed up to come forth in their purity, according to the truth which is in the Lamb, in the own due time of the Lord, unto the house of Israel.
27 And I, Nephi, heard and bear record, that the name of the apostle of the Lamb was
John, according to the word of the angel." (B. of M. 1 Nephi 14: 23-27)
Notice it says "the Lord hath ordained the apostle of the Lamb of God that he should write them...and the name of the apostle of the Lamb was John". A further reading in context makes it clear that it's talking about the revelation of John.
This is why I personally accept John's writings and his authority to write them.