webRequest.onAuthRequired listeners can provide authentication credentials.

chrome/browser/extensions/extension_webrequest_api_constants.cc

Index: chrome/browser/extensions/extension_webrequest_api_constants.cc
diff --git a/chrome/browser/extensions/extension_webrequest_api_constants.cc b/chrome/browser/extensions/extension_webrequest_api_constants.cc
index 63a980aa649f5d88da5973e9e2fa77222883cfc8..82e5fb7462213de1bea24e9ba68c33d2f973039c 100644
--- a/chrome/browser/extensions/extension_webrequest_api_constants.cc
+++ b/chrome/browser/extensions/extension_webrequest_api_constants.cc
@@ -29,6 +29,9 @@ const char kHeaderValueKey[] = "value";
 const char kIsProxyKey[] = "isProxy";
 const char kSchemeKey[] = "scheme";
 const char kRealmKey[] = "realm";
+const char kAuthCredentialsKey[] = "authCredentials";
+const char kUsernameKey[] = "username";
+const char kPasswordKey[] = "password";
 
 const char kOnBeforeRedirect[] = "experimental.webRequest.onBeforeRedirect";
 const char kOnBeforeRequest[] = "experimental.webRequest.onBeforeRequest";