I found windows TACACS applicaton which is working great with cisco switch and router.
http://tacacs.net/
http://heggel4.wordpress.com/2012/12/06/install-and-configure-tacacs-net/
Now, I have an issue when I try to add PI into TACACS.
From PI 1.2 it is very straighforward like below that AAA mode enabled and fallback as local user.

In TACACS+ section from PI, I put ip address, port, shared secret. I am not sure authentication type (PAP, CHAP) I selected CHAP, but there is no password column that I can fill in.

In the other hand, From TACACS.net software, there is CHAP password section, which I don't know.
<Name>user</Name>
<LoginPassword ClearText="kchefbrs" DES=""> </LoginPassword>
<EnablePassword ClearText="" DES=""></EnablePassword>
<CHAPPassword ClearText="" DES=""> </CHAPPassword>
<OutboundPassword ClearText="" DES=""> </OutboundPassword>
Then when I tried to log in, I got message like below, which is not "invalid username and password". When I googled it, some people mentioned about virtual domain. However, no luck.

Anybody has same issues?