basic_auth.go

package mux

import (
	"crypto/subtle"
	"encoding/base64"
	"net/http"
	"strconv"
)

// Accounts defines a key/value for user/pass list of authorized logins.
type Accounts map[string]string

type authPair struct {
	value string
	user  string
}

type authPairs []authPair

func (a authPairs) searchCredential(authValue string) (string, bool) {
	if authValue == "" {
		return "", false
	}
	for _, pair := range a {
		if subtle.ConstantTimeCompare([]byte(pair.value), []byte(authValue)) == 1 {
			return pair.user, true
		}
	}
	return "", false
}

// BasicAuthForRealm returns a Basic HTTP Authorization middleware. It takes as arguments a map[string]string where
// the key is the user name and the value is the password, as well as the name of the Realm.
// If the realm is empty, "Authorization Required" will be used by default.
// (see http://tools.ietf.org/html/rfc2617#section-1.2)
func BasicAuthForRealm(accounts Accounts, realm string) http.HandlerFunc {
	if realm == "" {
		realm = "Authorization Required"
	}
	realm = "Basic realm=" + strconv.Quote(realm)
	pairs := processAccounts(accounts)
	return func(w http.ResponseWriter, r *http.Request) {
		// Search user in the slice of allowed credentials
		_, found := pairs.searchCredential(r.Header.Get("Authorization"))
		if !found {
			// Credentials doesn't match, we return 401 and abort handlers chain.
			w.Header().Set("WWW-Authenticate", realm)
			w.WriteHeader(http.StatusUnauthorized)
			Stop(r)
			return
		}
	}
}

// BasicAuth returns a Basic HTTP Authorization middleware. It takes as argument a map[string]string where
// the key is the user name and the value is the password.
func BasicAuth(accounts Accounts) http.HandlerFunc {
	return BasicAuthForRealm(accounts, "")
}

func processAccounts(accounts Accounts) authPairs {
	length := len(accounts)
	pairs := make(authPairs, 0, length)
	for user, password := range accounts {
		value := authorizationHeader(user, password)
		pairs = append(pairs, authPair{
			value: value,
			user:  user,
		})
	}
	return pairs
}

func authorizationHeader(user, password string) string {
	base := user + ":" + password
	return "Basic " + base64.StdEncoding.EncodeToString([]byte(base))
}