If you want to bypass log on screen when you first time access obiee page through launch url i.e.http://localhost/analytics then here is solution.
Locate analytics virtual folder (C:\OracleBI\web\app\) in this folder replace default.asp page with following.
I am assuming you have anonymous user exists and particular user role has assigned some dashboards.
##%Response.Redirect("saw.dll?Dashboard?NQUser=Anonymous_user&NQPassword=Anonymous_user");%##
Replace default.jsp contents with following
##% response.sendRedirect("saw.dll?Dashboard?NQUser=Anonymous_user&NQPassword=Anonymous_user");%##
Please replace ## with < 'or' > respectively as shown in following figure
When ever users access obiee launch url , it bypasses logon screen and redirect to dashboard.