Add bypass of herokuapp access restriction (#85)

Refs teamniteo/ops#2359

Author: zupo

README.rst

@@ -47,7 +47,10 @@ Usage example for tweens::
 
 The ``pyramid_heroku.herokuapp_access`` tween depends on
 ``pyramid_heroku.client_addr`` tween and it requires you to list allowlisted IPs
-in the ``pyramid_heroku.herokuapp_allowlist`` setting.
+in the ``pyramid_heroku.herokuapp_allowlist`` setting. A bypass is possible
+by setting the `HEROKUAPP_ACCESS_BYPASS` environment variable to a secret value
+and then sending a request with the `HEROKUAPP_ACCESS_BYPASS` header set to the
+same secret value.
 
 The ``pyramid_heroku.client_addr`` tween sets request.client_addr to an IP we
 can trust. It handles IP spoofing via ``X-Forwarded-For`` headers and

pyramid_heroku/herokuapp_access.py

@@ -3,10 +3,14 @@
 from pyramid.response import Response
 
 import logging
+import os
 
 
 def includeme(config):
-    config.add_tween("pyramid_heroku.herokuapp_access.HerokuappAccess")
+    config.add_tween(
+        "pyramid_heroku.herokuapp_access.HerokuappAccess",
+        under="pyramid_heroku.client_addr.ClientAddr",
+    )
 
 
 class HerokuappAccess(object):
@@ -20,6 +24,8 @@ class HerokuappAccess(object):
     tween.
     """
 
+    import os
+
     def __init__(self, handler, registry):
         self.handler = handler
         self.registry = registry
@@ -30,6 +36,23 @@ def __call__(self, request):
             "pyramid_heroku.herokuapp_allowlist", ""
         ).split("\n")
 
+        if os.environ.get("HEROKUAPP_ACCESS_BYPASS"):
+            if request.headers.get("HEROKUAPP_ACCESS_BYPASS") == os.environ.get(
+                "HEROKUAPP_ACCESS_BYPASS"
+            ):
+                if request.registry.settings.get("pyramid_heroku.structlog"):
+                    import structlog
+
+                    logger = structlog.getLogger(__name__)
+                    logger.info(
+                        "Herokuapp access bypassed", user_ip=request.client_addr
+                    )
+                else:
+                    logger = logging.getLogger(__name__)
+                    logger.info(f"Herokuapp access bypassed by {request.client_addr}")
+
+                return self.handler(request)
+
         if (
             "herokuapp.com" in request.headers["Host"]
             and request.client_addr not in allowlisted_ips

pyramid_heroku/tests/test_herokuapp_access.py

@@ -5,6 +5,7 @@
 
 import logging
 import mock
+import os
 import structlog
 import unittest
 
@@ -66,7 +67,7 @@ def test_non_allowlisted_ip(self):
         assert not self.handler.called, "handler should not be called"
         self.assertEqual(len(tweens_handler.records), 1)
         self.assertEqual(
-            "Denied Herokuapp access for Host foo.herokuapp.com and IP 6.6.6.6",  # noqa
+            "Denied Herokuapp access for Host foo.herokuapp.com and IP 6.6.6.6",
             tweens_handler.records[0].msg,
         )
         self.assertEqual(response.status_code, 403)
@@ -101,3 +102,46 @@ def test_herokuapp_allowlist_empty(self):
 
         HerokuappAccess(self.handler, self.request.registry)(self.request)
         assert not self.handler.called, "handler should not be called"
+
+    @mock.patch.dict(os.environ, {"HEROKUAPP_ACCESS_BYPASS": "foo"})
+    def test_herokuapp_access_bypass(self):
+        "The IP check can be bypassed by setting a correct header."
+        from pyramid_heroku.herokuapp_access import HerokuappAccess
+
+        self.request.client_addr = "6.6.6.6"
+        self.request.headers = {
+            "Host": "foo.herokuapp.com",
+            "HEROKUAPP_ACCESS_BYPASS": "foo",
+        }
+
+        # structlog version
+        HerokuappAccess(self.handler, self.request.registry)(self.request)
+        self.handler.assert_called_with(self.request)
+        self.assertEqual(len(tweens_handler.records), 1)
+        self.assertEqual("Herokuapp access bypassed", tweens_handler.records[0].msg)
+
+        # standard logging version
+        self.request.registry.settings["pyramid_heroku.structlog"] = False
+        tweens_handler.clear()
+        HerokuappAccess(self.handler, self.request.registry)(self.request)
+        self.handler.assert_called_with(self.request)
+        self.assertEqual(len(tweens_handler.records), 1)
+        self.assertEqual(
+            "Herokuapp access bypassed by 6.6.6.6",
+            tweens_handler.records[0].msg,
+        )
+
+    @mock.patch.dict(os.environ, {"HEROKUAPP_ACCESS_BYPASS": "foo"})
+    def test_herokuapp_access_bypass_invalid(self):
+        "Invalid bypass code is rejected."
+        from pyramid_heroku.herokuapp_access import HerokuappAccess
+
+        self.request.client_addr = "6.6.6.6"
+        self.request.headers = {
+            "Host": "foo.herokuapp.com",
+            "HEROKUAPP_ACCESS_BYPASS": "bar",
+        }
+        self.request.registry.settings = {}
+
+        HerokuappAccess(self.handler, self.request.registry)(self.request)
+        assert not self.handler.called, "handler should not be called"