It would seem that it is sometimes necessary to be inauthentic in order be virtuous because the good man seeks perfection and no man is perfect. An ethical life is grounded in habits and some habits are good while others are bad. Thus, at times, the good man must thwart his own desires in the pursuit of justice, and authenticity is to live in accordance with one's own desires. Therefore it is sometimes necessary to be inauthentic in order to be virtuous.
On the contrary, a tedious old fool says, "This above all: to thine ownself be true."
I answer that, It is never necessary to be inauthentic in order to be virtuous, for the desire for perfection is the mark of the good man, and he who breaks with the bad habits that he has in order to acquire better habits that are not yet his is living in accordance with a desire that is higher, and thus more virtuous, than the man who is content to be himself as he is. Virtue is not a state but a power; one is never in a good place but, when virtuous, on a good way. A man is only truly himself insofar as he betters himself.