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[eluser]skunkbad[/eluser]
[quote author="Josssi" date="1334433070"]I am using library tank_auth. After sending correct username and password is created session.[/quote]

You going to want to find out the name of the cookie, or find out what tank auth is setting for a cookie, and unset it. I don't use tank auth, so I can't be more specific. Perhaps somebody else will answer.