Check the following links: -
Hope these may help you!
I was actually referring to using the command tabcmd login to login to the server. The Tableau Server Administrator Guide mentions the server and username information is stored in a cookie; however, I'm still not sure exactly where that location is. The problem is that it seems the Tableau Server Session is either timing out or the server information is not being stored/kept in the cookie. Seems I may have to open a Case with Tableau Support to figure this out.
In Internet Explorer cookie files are in the "cookies" folder:
"C:\Documents and Settings\user\Cookies".
Cookies are saved in browser. You have to check that which browser you are using & then find the location of your cookies folder.
If you want to save credentials then here is all the commands: - http://downloads.tableausoftware.com/quickstart/server-guides/server_tabcmd6.0.pdf
Hope this may help you!
Here is the answer I was looking for, provided by Tableau Support: "
In order for tabcmd functions to operate correctly,tabcmd must first be logged into Tableau Server, which stores an authentication token in the following folder: C:\Users\<Tableau Server User Account>\AppData\Roaming\Tableau\tabcmd.txt. An authentication token is stored so subsequent commands can be run without having to log in again. This token remains valid for five minutes after the last command that used it."
So the location is C:\Users\<Tableau Server User Account>\AppData\Roaming\Tableau\tabcmd.txt