diff --git a/app.py b/app.py
index 18b64c2..ba75393 100644
--- a/app.py
+++ b/app.py
@@ -1,7 +1,9 @@
-import logging
+import hmac
 import json
+import logging
+import os
 
-from flask import (Flask, request, jsonify)
+from flask import (Flask, request, jsonify, abort)
 
 from ltsdb_json import LTS
 
@@ -23,6 +25,8 @@ def report():
     n_dp = 0
     for d in data:
         d["description"]["remote_addr"] = request.remote_addr
+        d["description"]["node"] = verify_node(d)
+
         log.info("received %s", json.dumps(d))
         ts = LTS(d["description"])
         for dp in d["data"]:
@@ -31,3 +35,32 @@ def report():
             n_dp += 1
         n_ts += 1
     return jsonify({ "success": True, "timeseries": n_ts, "datapoints": n_dp })
+
+def verify_node(d):
+    node = d["auth"]["node"]
+    timestamp = d["auth"]["timestamp"]
+    digest1 = d["auth"]["hmac"]
+    if "/" in node:
+        raise ValueError("invalid node name %s", node)
+    try:
+        log.info("gettingg client config from %s", "config/" + node)
+        with open("config/" + node) as fh:
+            node_conf = json.load(fh)
+    except Exception as e:
+        log.warning("got %s opening %s", e, "config/" + node)
+        abort(401, "unknown client")
+    last = node_conf["last"]
+    for key in node_conf["keys"]:
+        msg = (node + " " + str(timestamp)).encode("UTF-8")
+        hmac2 = hmac.new(key.encode("UTF-8"), msg, "SHA-256")
+        digest2 = hmac2.hexdigest()
+        if hmac.compare_digest(digest1, digest2):
+            if timestamp > node_conf["last"]:
+                node_conf["last"] = timestamp
+                os.replace("config/" + node, "config/" + node + ".old")
+                with open("config/" + node, "w") as fh:
+                    json.dump(node_conf, fh) # XXX
+                return node
+            else:
+                abort(409, "timestamp out of sync")
+    abort(401, "auth failed")