webRequest.onAuthRequired listeners can provide authentication credentials.

chrome/browser/extensions/extension_webrequest_api_constants.h

Index: chrome/browser/extensions/extension_webrequest_api_constants.h
diff --git a/chrome/browser/extensions/extension_webrequest_api_constants.h b/chrome/browser/extensions/extension_webrequest_api_constants.h
index 4e3318f6046ecc73b52e1356de014ba0420f1093..e58d17e750ad20c4fa19f0263a58947d31f4d5f1 100644
--- a/chrome/browser/extensions/extension_webrequest_api_constants.h
+++ b/chrome/browser/extensions/extension_webrequest_api_constants.h
@@ -35,6 +35,9 @@ extern const char kHeaderValueKey[];
 extern const char kIsProxyKey[];
 extern const char kSchemeKey[];
 extern const char kRealmKey[];
+extern const char kAuthCredentialsKey[];
+extern const char kUsernameKey[];
+extern const char kPasswordKey[];
 
 // Events.
 extern const char kOnAuthRequired[];