Although "traditionally" ascribed to Rabbi Shimon bar Yochai zt"l, the Zohar has been beset with controversy about its authorship since it was discovered and published by R' Moshe de Leon. Notably there is a report cited below in the name of R' Moshe de Leon's widow's admitting that her late husband had authored the work himself.
a rich man of Avila, named Joseph, offered [de Leon's] widow, who had been left without means, a large sum of money for the original from which her husband had made the copy; and she then confessed that her husband himself was the author of the work. She had asked him several times, she said, why he had chosen to credit his own teachings to another, and he had always answered that doctrines put into the mouth of the miracle-working Simeon ben Yohai would be a rich source of profit. (Jewish Encyclopedia, see sources there)
What does contemporary Rabbinic and/or Academic scholarship have to say on the question of whether R de Leon himself composed the Zohar and to how much credibility is given to his widow's testimony?
Note this question does not ask if Rabbi Shimon Bar Yochai wrote it. That question was asked separately.