I've installed on TFS (on prem) 2017 update 3. When browsing to the extension tab under build there is only an error message displayed: TF400813: Resource not available for anonymous access. Client authentication required. 
I've installed on TFS (on prem) 2017 update 3. When browsing to the extension tab under build there is only an error message displayed:
TF400813: Resource not available for anonymous access. Client authentication required.