You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: socks5.go
    path of file: ./repos/plumber/vendor/golang.org/x/net/proxy
    
    the code of the file until where you have to start completion: // Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package proxy

import (
	"context"
	"net"

	"golang.org/x/net/internal/socks"
)

// SOCKS5 returns a Dialer that makes SOCKSv5 connections to the given
// address with an optional username and password.
// See RFC 1928 and RFC 1929.
func SOCKS5(network, address string, auth *Auth, forward Dialer) (Dialer, error) {
	d := socks.NewDialer(network, address)
	if forward != nil {
		if f, ok := forward.(ContextDialer); ok {
			d.ProxyDial = func(ctx context.Context, network string, address string) (net.Conn, error) {
				retur
    
func SOCKS5(network, address string, auth *Auth, forward Dialer) (Dialer, error) {
	d := socks.NewDialer(network, address)
	if forward != nil {
		if f, ok := forward.(ContextDialer); ok {
			d.ProxyDial = func(ctx context.Context, network string, address string) (net.Conn, error) {
				return f.DialContext(ctx, network, address)
			}
		} else {
			d.ProxyDial = func(ctx context.Context, network string, address string) (net.Conn, error) {
				return dialContext(ctx, forward, network, address)
			}
		}
	}
	if auth != nil {
		up := socks.UsernamePassword{
			Username: auth.User,
			Password: auth.Password,
		}
		d.AuthMethods = []socks.AuthMethod{
			socks.AuthMethodNotRequired,
			socks.AuthMethodUsernamePassword,
		}
		d.Authenticate = up.Authenticate
	}
	return d, nil
}