Problem utama otentifikasi ssh-key di Centos 6.x tidak jalan adalah selinuxnya di set secara enforced. Trik ini yang sering saya lupa :(. Caranya sebenarnya mudah cukup disable atau set ke mode permassive.

Dari:

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
SELINUX=enforcing# SELINUXTYPE= can take one of these two values:
# targeted - Targeted processes are protected,
# mls - Multi Level Security protection.
SELINUXTYPE=targeted

Ke

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
SELINUX=permissive
# SELINUXTYPE= can take one of these two values:
# targeted - Targeted processes are protected,
# mls - Multi Level Security protection.
SELINUXTYPE=targeted

Reload dengan

# setenforce 0

kemudian cek dengan:

# sestatus 
SELinux status:                 enabled
SELinuxfs mount:                /selinux
Current mode:                   permissive
Mode from config file:          permissive
Policy version:                 24
Policy from config file:        targeted

Note: selinux tetap jalan, hanya saja ssh-key sudah bisa aktif.