In the meantime, would you like to embed the username and password directly in your viz? So no one has to login.
This might help you for the moment: http://mkt.tableausoftware.com/downloads/embedding_views.pdf
Awaiting your answer.
Lénaïc RIÉDINGER, Global Community Engineer Tableau
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If you don't mind can you share your code. you should be able to send the req second time without the tickets.