Add /auth/api/v1/server/info endpoints.

server/auth/info/info.go

Index: server/auth/info/info.go
diff --git a/server/auth/info/info.go b/server/auth/info/info.go
new file mode 100644
index 0000000000000000000000000000000000000000..bbccabc9be6c109ff3ff07177de55cdf13c808d9
--- /dev/null
+++ b/server/auth/info/info.go
@@ -0,0 +1,77 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Package info exposes /auth/api/v1/server/info URL and allows to query it.
+//
+// This endpoint is used by luci services to advertise service account names
+// they use (among other things).
+package info
+
+import (
+	"encoding/json"
+	"net/http"
+	"time"
+
+	"github.com/julienschmidt/httprouter"
+	"golang.org/x/net/context"
+
+	"github.com/luci/luci-go/server/auth/internal"
+	"github.com/luci/luci-go/server/middleware"
+	"github.com/luci/luci-go/server/proccache"
+)
+
+// ServiceInfo describes JSON format of /auth/api/v1/server/info response.
+type ServiceInfo struct {
+	AppID              string `json:"app_id,omitempty"`
+	AppRuntime         string `json:"app_runtime,omitempty"`
+	AppRuntimeVersion  string `json:"app_runtime_version,omitempty"`
+	AppVersion         string `json:"app_version,omitempty"`
+	ServiceAccountName string `json:"service_account_name,omitempty"`
+}
+
+type proccacheKey string
+
+// FetchServiceInfo fetches information about the service at given URL.
+//
+// Uses proccache to cache it locally for 1 hour.
+func FetchServiceInfo(c context.Context, serviceURL string) (*ServiceInfo, error) {
+	info, err := proccache.GetOrMake(c, proccacheKey(serviceURL), func() (interface{}, time.Duration, error) {
+		info := &ServiceInfo{}
+		err := internal.FetchJSON(c, info, func() (*http.Request, error) {
+			return http.NewRequest("GET", serviceURL+"/auth/api/v1/server/info", nil)
+		})
+		if err != nil {
+			return nil, 0, err
+		}
+		return info, time.Hour, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return info.(*ServiceInfo), nil
+}
+
+// ServiceInfoCallback is called by /auth/api/v1/server/info handler.
+type ServiceInfoCallback func(context.Context) (ServiceInfo, error)
+
+// InstallHandlers installs handler that serves info provided by the callback.
+func InstallHandlers(r *httprouter.Router, base middleware.Base, cb ServiceInfoCallback) {
+	handler := func(c context.Context, w http.ResponseWriter, r *http.Request, p httprouter.Params) {
+		var response struct {
+			ServiceInfo
+			Error string `json:"error,omitempty"`
+		}
+		info, err := cb(c)
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			response.Error = err.Error()
+		} else {
+			w.WriteHeader(http.StatusOK)
+			response.ServiceInfo = info
+		}
+		json.NewEncoder(w).Encode(response)
+	}
+	r.GET("/auth/api/v1/server/info", base(handler))
+}