A few hours ago I commented on ideas proposed by Bri Hatch:
On the other hand two checks may cause severe performance impact.  In fact libwrap authentication is slower than TLS handshake while being a lot less secure.

I gave it a second thought and I decided to implement the feature as proposed by Bri.

Feel free to try a beta version:
ftp://ftp.stunnel.org/stunnel/stunnel-4.38b1.tar.gz
It still needs an update of the manual page...

Mike