More informative error message when LDAP messes up

authens/shortcuts.py

@@ -36,7 +36,10 @@ def fetch_cas_account(cas_login):
     if not res:
         return None
 
+    if len(res) != 1:
+        raise RuntimeError("LDAP returned too many results: {}".format(res))
     (res,) = res
+
     assert _extract_ldap_info(res, "uid") == cas_login
     return {
         "cn": _extract_ldap_info(res, "cn"),