Fix Bearer auth decode

auth.go

@@ -48,7 +48,7 @@ func handleAuthenticate(w http.ResponseWriter, req *http.Request) {
 
 	if *enableBearerAuth {
 		if auth := req.Header.Get("Authorization"); strings.HasPrefix(auth, "Bearer ") {
-			key, _ := base64.StdEncoding.DecodeString(auth)
+			key, _ := base64.StdEncoding.DecodeString(auth[7:])
 			if username, ok := tokens[string(key)]; ok {
 				status = http.StatusOK
 				log.Printf("auth(%s) -> ok", username)