I disagree that it's been "proven authentic". It has not been falsified is the best we can say right now. No one can prove it's a fraud, forgery, fake, or a work of art. We don't know.
The evidence leans heavily toward it being of first century provenance and that at sometime in it's existence it was in an area in a 50 mile radius around Jerusalem, had plants that were native to that area placed on it, and had the portion of it that was the backside of the dorsal image (and on the front of the cloth under the feet of the image) laid on a surface that had stone dust from Travertine Aragonite that is unique to quarries to the east of Jerusalem and consistent with that found in the traditional sites associated with Christ's tomb.
I'd go a bit further than that, inasmuch as there are a number of features present in this artefact which are consistent with the genuine article.
1) Wet-bench and spectrographic analysis does not show either quantity of or distribution of any known paint pigments in sufficient quantity to have created the image.
2) Details of the body inconsistent with the best available knowledge / belief at the time of a forger, but consistent with what we know now (placement of holes in wrists; inward curving of thumbs).
3) Demonstrated presence of breakdown products of blood -- blood type is thought to match Sudarium, as well as the shape of some of the stains; and the Sudarium has a separate documnented history and provenance. (How would that be faked?)
4) Presence of pollen and other plant materials, some of which are from plants in the vicinity of Jerusalem, and which blossom / release pollen only at the same time of year as Good Friday / Easter / Passover.
5) 3-D imaging inherent in the shroud's image, which was unknown at the time of the supposed forging.
6) The image is a photographic negative, which was unknown at the time of the supposed forging.
7) The image is the result of a Maillard reaction with the layers of the threads of the shroud, consistent with outgassing from a corpse; and inconsistent with painting. The image has survived a number of things done to the Shroud during its long history, including boiling in oil.
8) The "debunking" C-14 testing took a number of samples in an area where the Shroud had been "patched" (invisible French re-weaving) with newer cloth; the samples traversed a section of the Shroud where the relative proportion of old-to-new fiber changed from one sample to the next. This proportion was picked up by variations in the C-14 estimate of the age of each sample. Further tests on other parts of the Shroud are consistent with it being from the time of Christ, within experimental error.
9) The type of fabric and the method of weaving used are both consistent with the Shroud's authenticity as an artifact from ancient Israel.
These factors are all physically independent and they are all present simultaneously in the original object: they are not mere "suppositions."
Occam's razor suggests that the simplest explanation is the true one: whatever the mechanism for the formation of the image (including "as yet unknown"), the Shroud dates from the time of Christ and was really in close proximity to the bleeding body of a crucified person.
Cheers!