functions: Use Slack client lib for request validation (#4369)

* Use Slack client lib for request validation

* fix bad validation logic

* fix tests

* Add clarifying comment

* Fix lint

* Fix lint, take 2

* rm unused slackeventsapi package

functions/slack/main.py

@@ -12,12 +12,11 @@
 # limitations under the License.
 
 # [START functions_slack_setup]
-import hashlib
-import hmac
 import os
 
 from flask import jsonify
 import googleapiclient.discovery
+from slack.signature import SignatureVerifier
 
 
 kgsearch = googleapiclient.discovery.build(
@@ -29,19 +28,12 @@
 
 
 # [START functions_verify_webhook]
-# Python 3+ version of https://github.com/slackapi/python-slack-events-api/blob/master/slackeventsapi/server.py
 def verify_signature(request):
-    timestamp = request.headers.get('X-Slack-Request-Timestamp', '')
-    signature = request.headers.get('X-Slack-Signature', '')
+    request.get_data()  # Decodes received requests into request.data
 
-    req = str.encode('v0:{}:'.format(timestamp)) + request.get_data()
-    request_digest = hmac.new(
-        str.encode(os.environ['SLACK_SECRET']),
-        req, hashlib.sha256
-    ).hexdigest()
-    request_hash = 'v0={}'.format(request_digest)
+    verifier = SignatureVerifier(os.environ['SLACK_SECRET'])
 
-    if not hmac.compare_digest(request_hash, signature):
+    if not verifier.is_valid_request(request.data, request.headers):
         raise ValueError('Invalid request/credentials.')
 # [END functions_verify_webhook]
 

functions/slack/main_test.py

@@ -13,10 +13,12 @@
 
 import json
 import os
+import time
 
 import googleapiclient.discovery
 import mock
 import pytest
+from slack.signature import SignatureVerifier
 
 import main
 
@@ -28,8 +30,9 @@
 
 
 class Request(object):
-    def __init__(self, data=b''):
+    def __init__(self, data='', headers={}):
         self.data = data
+        self.headers = headers
 
     def get_data(self):
         return self.data
@@ -39,19 +42,28 @@ class TestGCFPySlackSample(object):
     def test_verify_signature_request_form_empty(self):
         with pytest.raises(ValueError):
             request = Request()
-            request.headers = {}
             main.verify_signature(request)
 
     def test_verify_signature_token_incorrect(self):
         with pytest.raises(ValueError):
-            request = Request()
-            request.headers = {'X-Slack-Signature': '12345'}
+            request = Request(headers={'X-Slack-Signature': '12345'})
             main.verify_signature(request)
 
     def test_verify_web_hook_valid_request(self):
         request = Request()
+        request.body = ''
+
+        now = str(int(time.time()))
+
+        verifier = SignatureVerifier(os.environ['SLACK_SECRET'])
+        test_signature = verifier.generate_signature(
+            timestamp=now,
+            body=''
+        )
+
         request.headers = {
-            'X-Slack-Signature': os.environ['SLACK_TEST_SIGNATURE']
+            'X-Slack-Request-Timestamp': now,
+            'X-Slack-Signature': test_signature
         }
         main.verify_signature(request)
 
@@ -77,14 +89,25 @@ def test_kg_search(self):
             entities = main.kgsearch.entities.return_value
             search = entities.search.return_value
             search.execute.return_value = example_response
+
             request = Request()
-            request.method = 'POST'
-            request.headers = {
-                'X-Slack-Signature': os.environ['SLACK_TEST_SIGNATURE']
-            }
             request.form = {
                 'text': 'lion'
             }
+            request.data = json.dumps(request.form)
+
+            now = str(int(time.time()))
+            verifier = SignatureVerifier(os.environ['SLACK_SECRET'])
+            test_signature = verifier.generate_signature(
+                timestamp=now,
+                body=request.data
+            )
+
+            request.method = 'POST'
+            request.headers = {
+                'X-Slack-Request-Timestamp': now,
+                'X-Slack-Signature': test_signature
+            }
 
             with mock.patch('main.jsonify', side_effect=json.dumps):
                 response = main.kg_search(request)

functions/slack/requirements.txt

@@ -1,3 +1,3 @@
 google-api-python-client==1.10.0
 flask==1.1.2
-slackeventsapi==2.2.0
+slackclient==2.7.3