webRequest.onAuthRequired listeners can provide authentication credentials.

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

Index: chrome/test/data/extensions/api_test/webrequest/framework.js
diff --git a/chrome/test/data/extensions/api_test/webrequest/framework.js b/chrome/test/data/extensions/api_test/webrequest/framework.js
index 635c2e3a1ab4eec2e07ff901e1b3770c0a9cdedb..939e63e2f406319ac3c8527749911db50b8c48b6 100644
--- a/chrome/test/data/extensions/api_test/webrequest/framework.js
+++ b/chrome/test/data/extensions/api_test/webrequest/framework.js
@@ -221,7 +221,7 @@ function initListeners(filter, extraInfoSpec) {
   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);