Auth Synaptic and Discover without password

/etc/polkit-1/localauthority/50-local.d/50-fancy-personal.pkla
--------------------------------------------------------------------
[Synaptic]
Identity=unix-group:sudo
Action=com.ubuntu.pkexec.synaptic
ResultAny=no
ResultInactive=no
ResultActive=yes

[Discover]
Identity=unix-group:sudo
Action=org.freedesktop.packagekit.*
ResultAny=no
ResultInactive=no
ResultActive=yes

For more, see man pklocalauthority

tips: to be as root login sudo -i