当搜索使用Go的HTTP基本身份验证示例时，我能找到的每个结果都不幸包含了过时的代码(即不使用Go1.4中引入的r.BasicAuth()功能)或不能防止定时攻击。本文介绍如何实现更安全的HTTP基本认证代码。

了解基本认证

你一定遇到，当通过浏览器访问一些URL时提示输入用户名和密码。再你输入用户名和密码后，浏览器发送包含Authorization头信息的HTTP请求至服务端，类似这样：

Authorization: Basic YWxpY2U6cGE1NXdvcmQ=

alice:pa55word
401 Unauthorized

基本认证可用于多种场景，但想要快速简单地保护低价值资源不受窥探时，它通常非常适合。为了更安全包含资源，还应该需要下列几种措施：

  • 使用HTTPS连接。如果不使用HTTPS，Authorization头信息可能被攻击者截获并解码，从使用凭证获取受保护资源。
  • 使用强密码。强密码含难被攻击者猜到或暴力破解。
  • 增加频率限制。避免攻击者采用暴力破解方式进行攻击。

另外，大多数编程语言和命令行工具(如curl和wget)以及web浏览器都支持基本的身份验证。

保护WEB应用

最简单保护应用的方式是创建一些中间件，主要实现三个方面内容：

  • 如果存在Authorization头信息，从中抽取用户名和密码。最简单可以通过Go1.4引入的r.BasicAuth() 方法实现。
  • 与期望正确的用户名和密码进行比较。为了避免时间攻击风险，应该使用subtle.ConstantTimeCompare()进行比较。

大多数语言使用==比较符两个字符串是否相等，如果第一个字符不同则直接返回。理论上这存在时间攻击的机会，对于大量请求比较平均响应时间的差异，从而猜测有多少字符已经正确，通过不断增加尝试次数，就可能获得正确的用户名和密码。为了避免时间攻击，我们使用subtle.ConstantTimeCompare()方法进行比较。

401 UnauthorizedWWW-Authenticate

根据上面的阐述，中间件实现代码类似下面代码：

func basicAuth(next http.HandlerFunc) http.HandlerFunc {return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {// 从请求头中出去用户和密码，如果认证请求头不存在或值无效，则ok为falseusername, password, ok := r.BasicAuth()if ok {// SHA-256算法计算用户名和密码usernameHash := sha256.Sum256([]byte(username))passwordHash := sha256.Sum256([]byte(password))expectedUsernameHash := sha256.Sum256([]byte("your expected username"))expectedPasswordHash := sha256.Sum256([]byte("your expected password"))// subtle.ConstantTimeCompare() 函数检查用户名和密码，相等返回1，否则返回0；// 重要的是先进行hash使得两者长度相等，从而避免泄露信息。usernameMatch := (subtle.ConstantTimeCompare(usernameHash[:], expectedUsernameHash[:]) == 1)passwordMatch := (subtle.ConstantTimeCompare(passwordHash[:], expectedPasswordHash[:]) == 1)// 如果比较结果正确，调用下一个处理器。// 最后调用return，为了让后面代码不被执行if usernameMatch && passwordMatch {next.ServeHTTP(w, r)return}}// If the Authentication header is not present, is invalid, or the// username or password is wrong, then set a WWW-Authenticate // header to inform the client that we expect them to use basic// authentication and send a 401 Unauthorized response.// 如果认证头不存在或无效，亦或凭证不正确，// 则需要设置WWW-Authenticate头信息并发送401未认证响应，为了通知客户端使用基本认证w.Header().Set("WWW-Authenticate", `Basic realm="restricted", charset="UTF-8"`)http.Error(w, "Unauthorized", http.StatusUnauthorized)})
}

上面代码使用sha256对用户名和密码进行哈希，并不是为了存储，而是为了获得等长字符串，使得比较时间为常量，降低碰撞风险。

realmrealm
realmrestricted

完整示例

下面看一个小型、功能完整的WEB应用示例。创建目录，然后增加main.go文件，初始化模块并使用mkcert工具创建本地信任证书：

$:~/gowork$ mkdir basic-auth-example            
$:~/gowork$ cd basic-auth-example/
$:~/gowork/basic-auth-example$ touch main.go
$:~/gowork/basic-auth-example$ go mod init basic-auth-example
go: creating new go.mod: module basic-auth-example
go: to add module requirements and sums:go mod tidy
$:~/gowork/basic-auth-example$ mkcert localhost
Note: the local CA is not installed in the system trust store.
Note: the local CA is not installed in the Firefox and/or Chrome/Chromium trust store.
Run "mkcert -install" for certificates to be trusted automatically ⚠️Created a new certificate valid for the following names 📜- "localhost"The certificate is at "./localhost.pem" and the key at "./localhost-key.pem" ✅It will expire on 10 July 2025 🗓$:~/gowork/basic-auth-example$ ls
go.mod  localhost-key.pem  localhost.pem  main.go

在main.go文件增加下面代码，期望的用户名和密码从环境变量中获取，和前文描述内容一致，使用中间件方式进行基本认证。

package mainimport ("crypto/sha256""crypto/subtle""fmt""log""net/http""os""time"
)type application struct {auth struct {username stringpassword string}
}func main() {app := new(application)// 从环境变量获取期望用户名和密码app.auth.username = os.Getenv("AUTH_USERNAME")app.auth.password = os.Getenv("AUTH_PASSWORD")if app.auth.username == "" {log.Fatal("basic auth username must be provided")}if app.auth.password == "" {log.Fatal("basic auth password must be provided")}// 创建HTTP服务器mux := http.NewServeMux()mux.HandleFunc("/unprotected", app.unprotectedHandler)mux.HandleFunc("/protected", app.basicAuth(app.protectedHandler))srv := &http.Server{Addr:         ":4000",Handler:      mux,IdleTimeout:  time.Minute,ReadTimeout:  10 * time.Second,WriteTimeout: 30 * time.Second,}log.Printf("starting server on %s", srv.Addr)err := srv.ListenAndServeTLS("./localhost.pem", "./localhost-key.pem")log.Fatal(err)
}// 保护资源处理器
func (app *application) protectedHandler(w http.ResponseWriter, r *http.Request) {fmt.Fprintln(w, "This is the protected handler")
}// 未保护资源处理器
func (app *application) unprotectedHandler(w http.ResponseWriter, r *http.Request) {fmt.Fprintln(w, "This is the unprotected handler")
}// 基本认证中间件模式
func (app *application) basicAuth(next http.HandlerFunc) http.HandlerFunc {return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {username, password, ok := r.BasicAuth()if ok {usernameHash := sha256.Sum256([]byte(username))passwordHash := sha256.Sum256([]byte(password))expectedUsernameHash := sha256.Sum256([]byte(app.auth.username))expectedPasswordHash := sha256.Sum256([]byte(app.auth.password))usernameMatch := (subtle.ConstantTimeCompare(usernameHash[:], expectedUsernameHash[:]) == 1)passwordMatch := (subtle.ConstantTimeCompare(passwordHash[:], expectedPasswordHash[:]) == 1)if usernameMatch && passwordMatch {next.ServeHTTP(w, r)return}}w.Header().Set("WWW-Authenticate", `Basic realm="restricted", charset="UTF-8"`)http.Error(w, "Unauthorized", http.StatusUnauthorized)})
}

现状使用临时一对环境变量启动应用：

AUTH_USERNAME=alice AUTH_PASSWORD=p8fnxeqj5a7zbrqp go run .
2023/04/10 11:38:00 starting server on :4000

curl访问

这时访问url:https://localhost:4000/protected,浏览器弹出提示认证表单。当然我们也可以通过curl验证认证是否正常工作。

$:~/Downloads$ curl -i https://localhost:4000/unprotected -k
HTTP/2 200 
content-type: text/plain; charset=utf-8
content-length: 32
date: Mon, 10 Apr 2023 05:42:52 GMTThis is the unprotected handler
$:~/Downloads$ curl -i https://localhost:4000/protected -k
HTTP/2 401 
content-type: text/plain; charset=utf-8
www-authenticate: Basic realm="restricted", charset="UTF-8"
x-content-type-options: nosniff
content-length: 13
date: Mon, 10 Apr 2023 05:44:25 GMTUnauthorized
$:~/Downloads$ curl -i -u alice:p8fnxeqj5a7zbrqp https://localhost:4000/protected -k
HTTP/2 200 
content-type: text/plain; charset=utf-8
content-length: 30
date: Mon, 10 Apr 2023 05:44:47 GMTThis is the protected handler
$:~/Downloads$ curl -i -u alice:wrongPa55word https://localhost:4000/protected -k
HTTP/2 401 
content-type: text/plain; charset=utf-8
www-authenticate: Basic realm="restricted", charset="UTF-8"
x-content-type-options: nosniff
content-length: 13
date: Mon, 10 Apr 2023 05:45:03 GMTUnauthorized

Go 客户端访问

req.SetBasicAuth("alice", "p8fnxeqj5a7zbrqp")
package mainimport ("fmt""io""log""net/http""time"
)func main() {client := http.Client{Timeout: 5 * time.Second}req, err := http.NewRequest(http.MethodGet, "https://localhost:4000/protected", http.NoBody)if err != nil {log.Fatal(err)}req.SetBasicAuth("alice", "p8fnxeqj5a7zbrqp")res, err := client.Do(req)if err != nil {log.Fatal(err)}defer res.Body.Close()resBody, err := io.ReadAll(res.Body)if err != nil {log.Fatal(err)}fmt.Printf("Status: %d\n", res.StatusCode)fmt.Printf("Body: %s\n", string(resBody))
}

总结

本文介绍了Go如何实现安全http基本认证，首先介绍原理，后面给出详细实现过程，最后通过curl和GO http客户端进行验证。详细内容参考：https://www.alexedwards.net/blog/basic-authentication-in-go