Have you ever looked up ‘inauthentic’ in the Oxford Online Dictionary? Hat tip to John Klotz.
Definition of inauthentic in English:
inauthentic
Syllabification: in·au·then·tic
Pronunciation: /ˌinôˈTHentik
/
ADJECTIVE
1 not in fact what it is said to be: the Holy Shroud of Turin is thought to have been proved inauthentic by radiocarbon dating
MORE EXAMPLE SENTENCES [ . . . ]
(emphasis mine) At least it’s “is thought to have been” rather than “has been.”