Currently, the websocket ClientEndpoint supports http proxy connection through 'http.proxyHost' and 'http.proxyPort' system properties, but does not support proxy authentication using username-password credentials. Provide proxy credentials support with parameters passed through 'http.proxyUser' and 'http.proxyPassword' system variables.
Currently, the WebSocket implmentation uses the standard Proxy API to obtain proxy configuration. 'http.proxyUser' and 'http.proxyPassword' are not part of that API. That is not a blocking issue but it is a concern.
Is this feature still needed? If so, I would like to work on it.
Yes, there is still interest in adding this feature to Tomcat. You might find this useful: https://blogs.oracle.com/wssfc/handling-proxy-server-authentication-requests-in-java On the basis that system properties are 'recommended' by Oracle - well, used in published examples at least, I'm less concerned.
*** This bug has been marked as a duplicate of bug 62312 ***