Have you ever looked up ‘inauthentic’  in the Oxford Online Dictionary? Hat tip to John Klotz.

 image

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.”