@Override
    public Builder proxyAuthentication(String proxyUserName, String proxyUserPassword) {
      final String userName = proxyUserName;
      final String password = proxyUserPassword;
      builder.proxyAuthenticator(
          (route, response) -> {
            String credential = Credentials.basic(userName, password);
            return response
                .request()
                .newBuilder()
                .header("Proxy-Authorization", credential)
                .build();
          });
      return this;
    }
Builder strategy for constructing an {@code OkHTTPRequestHandler}.
src/main/java/com/google/maps/OkHttpRequestHandler.java