Sometimes I may need authentication to run some programs in Xfce. If I passed the authentication, can the system remember the authentication during current session so that I won't need to input the password again?
This ain't really an Xfce issue. It depends on how you authenticate yourself. If with polkit then it depends on its rules, I think.
Debian based distros have gksu which can remember the authentication too.
Oh, thanks. I'll try it.
Also if you use 'sudo' with any distro, you can set the timeout for it and the commands that it can be used with (not with Ubuntu derived distros that, AFAIK, make it available for everything, which isn't very wise).