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

server/auth/info/info.go

+// 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"`
+        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.

[M-A Ruel, 2015/11/24 13:47:59]

Err, why not just do a HTTP 301 ?

[Vadim Sh., 2015/11/24 19:27:29]

What? Why? I don't understand.

This function will be called like FetchServiceInfo(c,
"https://chromium-swarm-dev.appspot.com") to get service account name of
swarming. I don't like hardcoding some arbitrary rules for hostname => service
account name conversion (since they have exceptions e.g. googleplex apps).

[M-A Ruel, 2015/11/24 19:31:34]

I mean, chromium-swarm-dev could redirect this API call to chrome-auth-dev? I
guess I miss something obvious here.

+//
+// 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))
+}