pass base64-decoded message on continuation to callback as error for xoauth2

lib/imap.js

@@ -661,13 +661,18 @@ ImapConnection.prototype.connect = function(loginCb) {
         var args = requests[0].cbargs,
             cmdstr = requests[0].cmdstr;
         if (!m) {
-          if (requests[0].cmd !== 'APPEND') {
-            err = new Error('Unexpected continuation');
+          if (requests[0].cmd === 'APPEND')
+            return requests[0].callback();
+          else {
+            var isXOAuth2 = (cmdstr.indexOf('AUTHENTICATE XOAUTH2') === 0),
+                msg = (isXOAuth2
+                       ? new Buffer(line.substr(2), 'base64').toString('utf8')
+                       : 'Unexpected continuation');
+            err = new Error(msg);
             err.level = 'protocol';
-            err.type = 'continuation';
+            err.type = (isXOAuth2 ? 'failure' : 'continuation');
             err.request = cmdstr;
-          } else
-            return requests[0].callback();
+          }
         } else if (m[1] !== 'OK') {
           // m[1]: error type
           // m[2]: resp-text-code