We are having difficulty getting Trusted Authentication to work and the issue is outlined in detail by them at the link below. Trusted Authenticaiton is working on the test server we are using, we have tested that and it works. We are unable to get their code working (see link below). We have checked all the forums, FAQ's and documentation and cannot find a solution. Any help / suggestions would be appreciated.
Answered your question @ stack exchange.
I'd also make 100% sure that the IP being used by php/apache is indeed trusted - maybe you can look at the access log in C:\ProgramData\Tableau\Tableau Server\data\tabsvc\logs\httpd to be sure?