Username and password are necessary for forward proxy authentication.
The initialization ran smoothly, but then I wasn't able to complete the activation process with the provided license key because the Server was unable to communicate with the Internet.
Having a look at the newly created tableau unprivileged user's .bash_profile file, I can see the two http_proxy and https_proxy parameters were correctly exported as namesake environment variables. Moreover, I specified the <host> using the IP value (e.g. 192.168.123.456), but it was automatically translated with the full hostname (e.g. frwprx.example.com).
Network sysadmins say the network traffic calls from the Tableau Server virtual machine to the forward proxy correctly refer to its <host> and <port> values, but they don't include <username> and <password>, even if they were specified during initialization.
Any help is really appreciated. Thank you in advance.