diff --git a/jwt_proxy/api.py b/jwt_proxy/api.py
index 8ad8c03..4675554 100644
--- a/jwt_proxy/api.py
+++ b/jwt_proxy/api.py
@@ -1,20 +1,13 @@
-from flask import Blueprint, abort, current_app, jsonify, request
+from flask import Blueprint, abort, current_app, jsonify, request, json as flask_json
 import jwt
 import requests
 import json
-from flask.json.provider import DefaultJSONProvider
 
 from jwt_proxy.audit import audit_HAPI_change
 
 blueprint = Blueprint('auth', __name__)
 SUPPORTED_METHODS = ('GET', 'POST', 'PUT', 'DELETE', 'OPTIONS')
 
-# Workaround no JSON representation for datetime.timedelta
-class CustomJSONProvider(DefaultJSONProvider):
-    @staticmethod
-    def default(obj):
-        return "Not_None"
-
 
 def proxy_request(req, upstream_url, user_info=None):
     """Forward request to given url"""
@@ -101,6 +94,14 @@ def smart_configuration():
 @blueprint.route("/settings/<string:config_key>")
 def config_settings(config_key):
     """Non-secret application settings"""
+
+    # workaround no JSON representation for datetime.timedelta
+    class CustomJSONEncoder(flask_json.JSONEncoder):
+        def default(self, obj):
+            return str(obj)
+
+    current_app.json_encoder = CustomJSONEncoder
+
     # return selective keys - not all can be be viewed by users, e.g.secret key
     blacklist = ("SECRET", "KEY")