improve error handling of custom auth callback

Author: rkusa

lib/framework/koa.js

@@ -89,9 +89,13 @@ function authenticate(passport, name, options, callback) {
     // `passportAuthenticate()` that we are ready.
     const _callback = callback
     callback = function(err, user, info, status) {
-      Promise.resolve(_callback(err, user, info, status))
-             .then(() => callback.resolve(false))
-             .catch(err => callback.reject(err))
+      try {
+        Promise.resolve(_callback(err, user, info, status))
+               .then(() => callback.resolve(false))
+               .catch(err => callback.reject(err))
+      } catch (err) {
+        callback.reject(err)
+      }
     }
   }