webRequest.onAuthRequired listeners can provide authentication credentials.

chrome/test/data/extensions/api_test/webrequest/framework.js

 // 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.
 
 var getURL = chrome.extension.getURL;
 var deepEq = chrome.test.checkDeepEq;
 var expectedEventData;
 var capturedEventData;
 var expectedEventOrder;
 var tabId;
@@ skipping 203 matching lines @@
       function(details) {
     return captureEvent("onSendHeaders", details);
   }, filter, intersect(extraInfoSpec, ["requestHeaders"]));
   chrome.experimental.webRequest.onHeadersReceived.addListener(
       function(details) {
     return captureEvent("onHeadersReceived", details);
   }, filter, intersect(extraInfoSpec, ["blocking", "responseHeaders"]));
   chrome.experimental.webRequest.onAuthRequired.addListener(
       function(details) {
     return captureEvent("onAuthRequired", details);
-  }, filter, intersect(extraInfoSpec, ["responseHeaders"]));
+  }, filter, intersect(extraInfoSpec, ["blocking", "responseHeaders"]));
   chrome.experimental.webRequest.onResponseStarted.addListener(
       function(details) {
     return captureEvent("onResponseStarted", details);
   }, filter, intersect(extraInfoSpec, ["responseHeaders"]));
   chrome.experimental.webRequest.onBeforeRedirect.addListener(
       function(details) {
     return captureEvent("onBeforeRedirect", details);
   }, filter, intersect(extraInfoSpec, ["responseHeaders"]));
   chrome.experimental.webRequest.onCompleted.addListener(
       function(details) {
@@ skipping 18 matching lines @@
   helper(chrome.experimental.webRequest.onBeforeRequest);
   helper(chrome.experimental.webRequest.onBeforeSendHeaders);
   helper(chrome.experimental.webRequest.onAuthRequired);
   helper(chrome.experimental.webRequest.onSendHeaders);
   helper(chrome.experimental.webRequest.onHeadersReceived);
   helper(chrome.experimental.webRequest.onResponseStarted);
   helper(chrome.experimental.webRequest.onBeforeRedirect);
   helper(chrome.experimental.webRequest.onCompleted);
   helper(chrome.experimental.webRequest.onErrorOccurred);
 }