basic auth for plugin

+// basic auth for plugin
+package auth
+
+// Example:
+// func SecretAuth(username, password string) bool {
+// 	if username == "astaxie" && password == "helloBeego" {
+// 		return true
+// 	}
+// 	return false
+// }
+// authPlugin := auth.NewBasicAuthenticator(SecretAuth)
+// beego.AddFilter("*","AfterStatic",authPlugin)
+
+import (
+	"encoding/base64"
+	"net/http"
+	"strings"
+
+	"github.com/astaxie/beego"
+	"github.com/astaxie/beego/context"
+)
+
+func NewBasicAuthenticator(secrets SecretProvider, Realm string) beego.FilterFunc {
+	return func(ctx *context.Context) {
+		a := &BasicAuth{Secrets: secrets, Realm: Realm}
+		if username := a.CheckAuth(ctx.Request); username == "" {
+			a.RequireAuth(ctx.ResponseWriter, ctx.Request)
+		}
+	}
+}
+
+type SecretProvider func(user, pass string) bool
+
+type BasicAuth struct {
+	Secrets SecretProvider
+	Realm   string
+}
+
+/*
+ Checks the username/password combination from the request. Returns
+ either an empty string (authentication failed) or the name of the
+ authenticated user.
+
+ Supports MD5 and SHA1 password entries
+*/
+func (a *BasicAuth) CheckAuth(r *http.Request) string {
+	s := strings.SplitN(r.Header.Get("Authorization"), " ", 2)
+	if len(s) != 2 || s[0] != "Basic" {
+		return ""
+	}
+
+	b, err := base64.StdEncoding.DecodeString(s[1])
+	if err != nil {
+		return ""
+	}
+	pair := strings.SplitN(string(b), ":", 2)
+	if len(pair) != 2 {
+		return ""
+	}
+
+	if a.Secrets(pair[0], pair[1]) {
+		return pair[0]
+	}
+	return ""
+}
+
+/*
+ http.Handler for BasicAuth which initiates the authentication process
+ (or requires reauthentication).
+*/
+func (a *BasicAuth) RequireAuth(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("WWW-Authenticate", `Basic realm="`+a.Realm+`"`)
+	w.WriteHeader(401)
+	w.Write([]byte("401 Unauthorized\n"))
+}