When trying to bypass a proxy to make Tableau Desktop connect directly to Tableau Server using OAuth, it is not possible to bypass the proxy even if the Tableau Server domain name and IP address is added to the environmental variable NO_PROXY. The connection continues to use the proxy.
If your proxy server has limited the access from the Tableau Desktop client PC or the access to Tableau Server, you may experience error messages from Tableau Desktop such as:
Exception thrown while attempting to get the oauth tokens: com.google.api.client.auth.oauth2.TokenResponseException: 503 Service Unavailable
POST https://<server name or ip address>/oauth2/v1/token
Exception thrown while attempting to get the oauth tokens: java.io.IOException: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 403 Forbidden"