/usr/share/man/man5/authorized_keys.5.gz is in openssh-server 1:5.9p1-5ubuntu1.10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man5/../man8/sshd.8.gz
/usr/share/man/man5/../man8/sshd.8.gz