From d244a1e02fd6cf5f705e261f32e08a10c53572dd Mon Sep 17 00:00:00 2001
From: Joseph Weston <joseph.weston08@gmail.com>
Date: Mon, 21 Nov 2016 16:13:50 +0100
Subject: [PATCH] allow `check_whitelist` to be a coroutine

Some authenticators may have whitelist checking that requires
async operations.
---
 jupyterhub/auth.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/jupyterhub/auth.py b/jupyterhub/auth.py
index 8ed982ee..a9f2620c 100644
--- a/jupyterhub/auth.py
+++ b/jupyterhub/auth.py
@@ -132,7 +132,9 @@ class Authenticator(LoggingConfigurable):
         if not self.validate_username(username):
             self.log.warning("Disallowing invalid username %r.", username)
             return
-        if self.check_whitelist(username):
+
+        whitelist_pass = yield gen.maybe_future(self.check_whitelist(username))
+        if whitelist_pass:
             return username
         else:
             self.log.warning("User %r not in whitelist.", username)