Implementing Trusted Tickets requires you to write a little bit of code IF you want the username passed to Tableau Server to be dynamic based on who just hit your web server.
99.9% of folks want this - If "Alex" logs into the Web Server, and your Web Server has authenticated you as "Alex", then we also want to tell Tableau Server that it's "Alex" requesting a report.
Even if you don't, some basic code is required to "merge" the trusted ticket you get back from Tableau Server with a second request you make to Tableau Server to actually ask for the report with the ticket.
The code that you'd write needs to "talk" to the mechanism that authenticated you. You'd need to understand the correct programmatic methods to ask your web server "Hey, who is this guy currently logged in?". Then you need to take that information and perform an HTTP POST against Tableau Server with it.
Since there are hundreds of authentication mechanisms out there, Tableau can't write sample code for each one - we leave it up to the customer to "know their own server tech", so to speak.
That being said, there ARE a few samples in Tableau\Tableau Server\7.0\extras\embedding that show you how you might approach this code-writing.
Sorry I can't give you a more straight-forward answer, but there really isn't one - it all depends on the authentication technology that you want Tableau Server to respect.
Hope this helps? Maybe a little?