Trusted ticket is available only on Tableau Server, but not yet for Tableau Online.
You can vote for this feature in the following thread : https://community.tableau.com/ideas/5589
I never hear about "custom-portal-sample", but it looks like pretty interesting!
My only concern is, the last commit was made 3 years ago, so I wonder if there is any compatibility issue with our latest REST API ? (3 years ago it should be REST API 2.4, and Tableau Online is currently using the REST API 3.6)