code: public Proxy setSocksUsername(String username) {
      verifyProxyTypeCompatibility(ProxyType.MANUAL);
      this.proxyType = ProxyType.MANUAL;
      this.socksUsername = username;
      return this;
    }
docs: Specifies a username for the SOCKS proxy. Supported by SOCKS v5 and above.
  
  @param username username for the SOCKS proxy
  @return reference to self