It sounds as though your application is sending an auth token as a header in the request to Tableau Server, is that correct?
Tableau Server doesn't accept username or password information as headers or url parameters for security reasons, so it would not be able to accept that token and pass it on to another service. If you are using the same OpenID provider for Tableau Server and for your app - your browser should be remembering and supplying the cookie needed to authenticate. Unless the browser is setting and passing 1st and 3rd party cookies, you'll be prompted to authenticate each time. Have you checked the browser settings?