ADDITIONAL SYSTEM INFORMATION :
Fedora 43, running Temurin 17, but reproducible on OpenJDK 17, and OpenJDK 21.

A DESCRIPTION OF THE PROBLEM :
We're trying to get javadoc to use an https proxy with basic authentication to fetch the oracle docs. Unfortunately, even when setting an empty scheme for jdk.http.auth.tunneling.disabledSchemes, the appropriate proxy authentication header is not set.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Use your own http proxy with basic authentication
2. Generate javadoc for Haha.java file:

    $ javadoc -J-Dhttps.proxyHost=localhost -J-Dhttps.proxyPort=8888 -J-Dhttps.proxUser=<user> -J-Dhttps.proxyPassword=<password> -link https://docs.oracle.com/en/java/javase/17/docs/api -J-Djdk.http.auth.tunneling.disabledSchemes="" -J-Djdk.http.auth.proxy.disabledSchemes="" Haha.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The http proxy connect goes through.
ACTUAL -
The http proxy connection fails with proxy authentication required (407). Also confirmed via wireshark that the Proxy-Authentication header is never passed in the proxy request from javadoc.

---------- BEGIN SOURCE ----------
// FIle is Haha.java
/**
 * class for testing javadoc
 */

public class Haha {
    /**
     * main method
     */
    public static void main(String[] args) {
        System.out.println("hello");
    }
}
---------- END SOURCE ----------