The ability to use the Google Big Query Service Account on Tableau Server is not currently built into the product.
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According to this document Allow Saved Access Tokens - Tableau , Tableau would allow managing oAuth credentials centrally and use a dedicated account for the connections. Would this mean we can use a Big Query service account or what is the use case you think they refer to in this document ?
As far as we experience, the standard Google Authentication screen is shown, but I don't see an option to select a sort of "dedicated account".