Authentic what? A cloth that shows the inexplicable image of a crucified man that bearing wounds that indicate the man the cloth covered experienced beating and execution in a manner that matches the supposed unique manner that the person Jeshua Bar Josef experienced approximately 2000 years ago? Yes.
Authentic in that scientific evidence shows that this Shroud is the shroud of one Jeshua Bar Josef and no other? No.
But the circumstantial evidence is simply overwhelming.
Even the FACE on the Shroud is very similar to the face presented as Christ's in Byzantine Icons and paintings going back to early Byzantine times. The likelihood that such a shroud would be carefully retained by Christ's early followers is not an unreasonable one.