When a user logs into sync, the appropriate cookies are retrieved so that

chrome/browser/chromeos/login/issue_response_handler.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/chromeos/login/issue_response_handler.h"
 
 #include <string>
 
 #include "base/stringprintf.h"
 #include "chrome/browser/net/chrome_url_request_context.h"
 #include "chrome/common/net/gaia/gaia_urls.h"
 #include "content/common/url_fetcher.h"
 #include "net/base/load_flags.h"
 
 namespace chromeos {
 
 // Overridden from AuthResponseHandler.
 bool IssueResponseHandler::CanHandle(const GURL& url) {
   return (url.spec().find(GaiaUrls::GetInstance()->issue_auth_token_url()) !=
           std::string::npos);
 }
 
 // Overridden from AuthResponseHandler.
 URLFetcher* IssueResponseHandler::Handle(
     const std::string& to_process,
     URLFetcher::Delegate* catcher) {
   VLOG(1) << "Handling IssueAuthToken response";
-  token_url_.assign(base::StringPrintf("%s%s",
-      GaiaUrls::GetInstance()->token_auth_url().c_str(), to_process.c_str()));
+  token_url_.assign(BuildTokenAuthUrlWithToken(to_process));
   URLFetcher* fetcher =
       new URLFetcher(GURL(token_url_), URLFetcher::GET, catcher);
   fetcher->set_load_flags(net::LOAD_DO_NOT_SEND_COOKIES);
   if (getter_) {
     VLOG(1) << "Fetching " << GaiaUrls::GetInstance()->token_auth_url();
     fetcher->set_request_context(getter_);
     fetcher->Start();
   }
   return fetcher;
 }
 
+// static
+std::string IssueResponseHandler::BuildTokenAuthUrlWithToken(
+    const std::string& token) {
+  const char kUrlFormat[] = "%s?"
+                            "continue=http://www.google.com/webhp&"
+                            "source=chromeos&"
+                            "auth=%s";
+  return base::StringPrintf(kUrlFormat,
+                            GaiaUrls::GetInstance()->token_auth_url().c_str(),
+                            token.c_str());
+}
+
 }  // namespace chromeos