Automatic Login with Local authentication

Hi all

I have a scenario where i can use only Local Authentication for my Tableau Server Installation.

I would like to implement something like this: user is logged in a custom webapplication (asp.net webapp using Membership for user authetication). I already use trusted authentication to embed some tableau  views into this custom webapplication.

What i'd like to do and i don't know how to do is this: i'd like to add a button in my application that opens Tableau Server Homepage, but i want first to authenticate user automatically against his own credentials stored into Tableau Server local authentication, then open the tableau server homepage (this is order to avoid user has to enter his username and password). How can i do this? Trusted authentication seems not to be a viable option 'cause it can be used only to embed a single view (as i actually do). And i do not have Active directory nor possibility to use OPENID cause server cannot browse internet.

Thanks in advance for any suggestion.