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: auth.go
    path of file: ./repos/goldfish/vendor/github.com/ncw/swift
    
    the code of the file until where you have to start completion: package swift

import (
	"bytes"
	"encoding/json"
	"net/http"
	"net/url"
	"strings"
)

// Auth defines the operations needed to authenticate with swift
//
// This encapsulates the different authentication schemes in use
type Authenticator interface {
	// Request creates an http.Request for the auth - return nil if not needed
	Request(*Connection) (*http.Request, error)
	// Respon
    
func (auth *v2Auth) Request(c *Connection) (*http.Request, error) {
	auth.Region = c.Region
	// Toggle useApiKey if not first run and not OK yet
	if auth.notFirst && !auth.useApiKeyOk {
		auth.useApiKey = !auth.useApiKey
	}
	auth.notFirst = true
	// Create a V2 auth request for the body of the connection
	var v2i interface{}
	if !auth.useApiKey {
		// Normal swift authentication
		v2 := v2AuthRequest{}
		v2.Auth.PasswordCredentials.UserName = c.UserName
		v2.Auth.PasswordCredentials.Password = c.ApiKey
		v2.Auth.Tenant = c.Tenant
		v2.Auth.TenantId = c.TenantId
		v2i = v2
	} else {
		// Rackspace special with API Key
		v2 := v2AuthRequestRackspace{}
		v2.Auth.ApiKeyCredentials.UserName = c.UserName
		v2.Auth.ApiKeyCredentials.ApiKey = c.ApiKey
		v2.Auth.Tenant = c.Tenant
		v2.Auth.TenantId = c.TenantId
		v2i = v2
	}
	body, err := json.Marshal(v2i)
	if err != nil {
		return nil, err
	}
	url := c.AuthUrl
	if !strings.HasSuffix(url, "/") {
		url += "/"
	}
	url += "tokens"
	req, err := http.NewRequest("POST", url, bytes.NewBuffer(body))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("User-Agent", c.UserAgent)
	return req, nil
}