netutil: add BasicAuth function

etcd ships it's own BasicAuth function and no longer requires
Go 1.4 to build.

pkg/netutil/netutil.go

@@ -15,10 +15,13 @@
 package netutil
 
 import (
+	"encoding/base64"
 	"log"
 	"net"
+	"net/http"
 	"net/url"
 	"reflect"
+	"strings"
 )
 
 var (
@@ -99,3 +102,36 @@ func URLStringsEqual(a []string, b []string) bool {
 
 	return URLsEqual(urlsA, urlsB)
 }
+
+// BasicAuth returns the username and password provided in the request's
+// Authorization header, if the request uses HTTP Basic Authentication.
+// See RFC 2617, Section 2.
+// Based on the BasicAuth method from the Golang standard lib.
+// TODO: use the standard lib BasicAuth method when we move to Go 1.4.
+func BasicAuth(r *http.Request) (username, password string, ok bool) {
+	auth := r.Header.Get("Authorization")
+	if auth == "" {
+		return
+	}
+	return parseBasicAuth(auth)
+}
+
+// parseBasicAuth parses an HTTP Basic Authentication string.
+// "Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==" returns ("Aladdin", "open sesame", true).
+// Taken from the Golang standard lib.
+// TODO: use the standard lib BasicAuth method when we move to Go 1.4.
+func parseBasicAuth(auth string) (username, password string, ok bool) {
+	if !strings.HasPrefix(auth, "Basic ") {
+		return
+	}
+	c, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(auth, "Basic "))
+	if err != nil {
+		return
+	}
+	cs := string(c)
+	s := strings.IndexByte(cs, ':')
+	if s < 0 {
+		return
+	}
+	return cs[:s], cs[s+1:], true
+}