diff --git a/lib/wsapi/auth_with_assertion.js b/lib/wsapi/auth_with_assertion.js
index b843d4614e44ad1260a02b1ba4f36db9873d9f8e..16c93816ee67f68fb1608b99f4c450e9a0fdbf11 100644
--- a/lib/wsapi/auth_with_assertion.js
+++ b/lib/wsapi/auth_with_assertion.js
@@ -43,7 +43,7 @@ exports.process = function(req, res) {
           if (!uid) return res.json({ success: false, reason: "internal error" });
           wsapi.authenticateSession(req.session, uid, 'assertion',
                                     req.ephemeral ? config.get('ephemeral_session_duration_ms') : undefined);
-          return res.json({ success: true });
+          return res.json({ success: true, userid: uid });
         });
       }
       else if (type === 'secondary') {
@@ -93,7 +93,7 @@ exports.process = function(req, res) {
           logger.info("successfully created primary acct for " + email + " (" + r.userid + ")");
           wsapi.authenticateSession(req.session, r.userid, 'assertion',
                                     req.ephemeral ? config.get('ephemeral_session_duration_ms') : undefined);
-          res.json({ success: true });
+          res.json({ success: true, userid: r.userid });
         });
       }).on('error', function(e) {
         logger.error("failed to create primary user with assertion for " + email + ": " + e);