secure.go shows the logic for the simple server. It has been divided into four functions:

• The requestHandler function to respond to incoming HTTP requests.
• The isAuthorized function to check if the incoming request is authorized.
• The getAuthorizedUser function to check if the token has an associated user. If the token does not have an associated user, then the token is considered to be invalid.
• The main function to start the server.

Now let's look at the code:

// secure/secure.go 
package main 
 
import ( 
    "fmt" 
    "log" 
    "net/http" 
    "strings" 
) 
 
var authTokens = map[string]string{ 
    "AUTH-TOKEN-1": "User 1", 
    "AUTH-TOKEN-2": "User 2", 
} 
 
// getAuthorizedUser tries to retrieve user for the given token. 
func getAuthorizedUser(token string) (string, error) { 
    var err error 
 
    user, valid := authTokens[token] 
    if !valid { 
        err = fmt.Errorf("Auth token '%s' does not exist.", token) 
    } 
 
    return user, err 
} 
 
// isAuthorized checks request to ensure that it has Authorization header 
// with defined value: "Bearer AUTH-TOKEN" 
func isAuthorized(r *http.Request) bool { 
    rawToken := r.Header["Authorization"] 
    if len(rawToken) != 1 { 
        return false 
    } 
 
    authToken := strings.Split(rawToken[0], " ") 
    if !(len(authToken) == 2 && authToken[0] == "Bearer") { 
        return false 
    } 
 
    user, err := getAuthorizedUser(authToken[1]) 
    if err != nil { 
        log.Printf("Error: %s", err) 
        return false 
    } 
 
    log.Printf("Successful request made by '%s'", user) 
    return true 
} 
 
var success = []byte("Received authorized request.") 
var failure = []byte("Received unauthorized request.") 
 
func requestHandler(w http.ResponseWriter, r *http.Request) { 
    if isAuthorized(r) { 
        w.Write(success) 
    } else { 
        w.WriteHeader(http.StatusUnauthorized) 
        w.Write(failure) 
    } 
} 
 
func main() { 
    http.HandleFunc("/", requestHandler) 
    fmt.Println("Starting server @ http://localhost:8080") 
    http.ListenAndServe(":8080", nil) 
}