Fix Proxy requiring Authentication usage

[lenaing]

Hello there,

This PR intends to fix proxy requiring authentication usage and wrong documentation about it.

I could not find a way to use proxy requiring an authentication with preemptive authentication enabled, even in a simple out-of-this-PR context.

Java is not my main language so there may be a more elegant / efficient way to fix this issue.

Kind regards,

Tested against both authenticated and unauthenticaded Squid

mysquid.conf

auth_param basic program /usr/lib/squid/basic_ncsa_auth /etc/squid/passwords
auth_param basic realm Squid proxy-caching web server
auth_param basic credentialsttl 24 hours
auth_param basic casesensitive off
acl authenticated proxy_auth REQUIRED
http_access allow authenticated
http_access deny all
dns_v4_first on
forwarded_for delete
via off
http_port 3128

Running the Squids

docker run -e TZ=UTC -p 3129:3128 ubuntu/squid:5.2-22.04_beta
docker run -e TZ=UTC -v /path/to/mysquid.conf:/etc/squid/squid.conf -v /path/to/mysquidpasswords:/etc/squid/passwords -p 3128:3128 ubuntu/squid:5.2-22.04_beta

Tests

pipeline {
    agent any

    stages {
        stage('Test') {
            steps {
                // No proxy
                httpRequest url: 'https://httpbin.org/'
                httpRequest url: 'https://httpbin.org/basic-auth/user/passwd', authentication: 'httpbin'
                // Proxy without authentication
                httpRequest url: 'https://httpbin.org/', httpProxy: 'http://127.0.0.1:3129'
                httpRequest url: 'https://httpbin.org/basic-auth/user/passwd', authentication: 'httpbin', httpProxy: 'http://127.0.0.1:3129'
                // Proxy with authentication
                httpRequest url: 'https://httpbin.org/', httpProxy: 'http://127.0.0.1:3128',  proxyAuthentication: 'proxy-auth'
                httpRequest url: 'https://httpbin.org/basic-auth/user/passwd', authentication: 'httpbin', httpProxy: 'http://127.0.0.1:3128',  proxyAuthentication: 'proxy-auth'
            }
        }
    }
}