Comment 7 for bug 505301

The attached trivial patch applies the wish I described above,
it informs more why authorized_keys is not being used.

The patch is tested for all error conditions it should report, both with default LogLevel INFO, as well as with DEBUG3.

Below detaild explanation what it does - and results of test.

It needs debug1 level to show conditions that are typical (missing authorized_keys), and it logs usually conditions that look like errors (i.e. .ssh/authorized_keys exists, but is inaccessible)

Examples of what will be in log for various use cases conditions:

rm .ssh/authorized_keys
Jan 10 05:22:48 lcwood sshd[15934]: debug1: unable to open public key file /home/rafal/.ssh/authorized_keys

chmod 000 .ssh/authorized_keys
Jan 10 05:19:26 lcwood sshd[15763]: authorized_keys ERROR: permission denied for opening user rafal authorized keys /home/rafal/.ssh/authorized_keys!

chmod 000 .ssh/
Jan 10 05:21:08 lcwood sshd[15817]: authorized_keys ERROR: permission denied for opening user rafal authorized keys /home/rafal/.ssh/authorized_keys!

mv .ssh .ssh-2
ln -s .ssh .ssh
Jan 10 05:26:40 lcwood sshd[16088]: authorized_keys ERROR: Can not access user rafal authorized keys /home/rafal/.ssh/authorized_keys - Too many levels of symbolic links (errno=40)!

And with option (/etc/ssh/sshd_config)
  LogLevel INFO
only the error conditions thes ones with ERROR are loged, since they are undexpted.