Whenever I come across the words "authentic", "authenticity", etc. in (modern) philosophy texts, the manner and context in which they are used often give me the impression that the author intended them in a sense (a "technical" sense?) that differs significantly from the one I am familiar with.
I would like to understand the concept of authenticity a lot better than I now do. IOW, I'm basically looking for the moral equivalent of a "Phenomenology of Authenticity for Dummies". (No primary sources please, not yet.)
Also, is there a generally accepted "locus classicus" for the "modern philosophy sense" of "authentic"/"authenticity", etc? (By "modern" I mean certainly the 20th century, but it wouldn't surprise me if such usage of "authentic", etc. went back to the 19th century or earlier.)