The accepted answer below is the correct one assuming (as I thought) that the server is v2.2.
Instead, I discovered the server is apache 2.4 instead, so the real solution was to use the new directives. Please see my comment below the accepted answer.
in mydomain.com/wp-admin I placed a .htaccess with something like
# note: the ip here is a fake order deny,allow deny from all allow from 192.168.1.101
But I now get a 403 error. The domain and IP here are fake, but the real IP I'm using is correct since I can see it form logs, that are something like:
www.example.com 192.168.1.101 - - [10/Jan/2017:10:51:52 +0100] "GET /wp-admin/ HTTP/1.1" 403 518 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:50.0) Gecko/20100101 Firefox/50.0"
So it's really strange, I should be able to enter. Any Idea?