LogDog: Use server/auth for authentication.

logdog/server/service/rt.go

+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package service
+
+import (
+        "net/http"
+        "strings"
+
+        commonAuth "github.com/luci/luci-go/common/auth"
+)
+
+type serviceModifyingTransport struct {
+        userAgent string
+}
+
+func (smt *serviceModifyingTransport) roundTripper(base http.RoundTripper) http.RoundTripper {

[iannucci, 2017/01/21 00:37:00]

this seems like maybe we should do this everywhere, somehow...

+        if base == nil {
+                base = http.DefaultTransport
+        }
+
+        return commonAuth.NewModifyingTransport(base, func(req *http.Request) error {
+                // Set a user agent based on our service. If an existing user agent is
+                // specified, add it onto the end of the string.
+                parts := make([]string, 0, 2)
+                for _, part := range []string{
+                        smt.userAgent,
+                        req.UserAgent(),
+                } {
+                        if part != "" {
+                                parts = append(parts, part)
+                        }
+                }
+                if len(parts) > 0 {
+                        req.Header.Set("User-Agent", strings.Join(parts, " / "))
+                }
+                return nil
+        })
+}