So, we are left with perhaps some authentic and/or infallible witnesses, but never a canon of inspired books.

St. Thomas answers by giving an extraordinarily helpful taxonomy of the different kinds of texts in sacred scripture, describing which texts contain which senses. 

Jay Dyer can say the Shahada. Yes, you heard me right. He can say the Shahada. That basically is the Nicene Creed of Islam. This must make Jay a Muslim.