diff --git a/reviewboard/admin/security_checks.py b/reviewboard/admin/security_checks.py
index 378bdd72c21a2621b99140a3c185d490ec141a9b..53f4297d205490d6da1344b2908a2c388825587e 100644
--- a/reviewboard/admin/security_checks.py
+++ b/reviewboard/admin/security_checks.py
@@ -13,6 +13,7 @@ from django.utils.translation import gettext_lazy as _
 from djblets.log import log_timed
 
 from reviewboard.admin.server import build_server_url
+from reviewboard.certs.manager import cert_manager
 
 
 _security_checks = OrderedDict()
@@ -252,7 +253,10 @@ class ServerExecutableFileCheck(BaseExecutableFileCheck):
                            f'executable file at {url}',
                            default_level=logging.INFO,
                            logger=logger):
-                data = urlopen(url).read()
+                data = urlopen(
+                    url,
+                    **cert_manager.build_urlopen_kwargs(url=url),
+                ).read()
         except HTTPError as e:
             # An HTTP 403 is also an acceptable response
             if e.code == 403:
@@ -341,7 +345,10 @@ class BrowserExecutableFileCheck(BaseExecutableFileCheck):
                        f'attachment at {url}',
                        default_level=logging.INFO,
                        logger=logger):
-            headers = urlopen(url).info()
+            headers = urlopen(
+                url,
+                **cert_manager.build_urlopen_kwargs(url=url),
+            ).info()
 
         return headers.get('Content-Disposition', '').startswith('attachment')
 
diff --git a/reviewboard/cmdline/rbsite.py b/reviewboard/cmdline/rbsite.py
index f0f26826a6746e9f8c3edb10edfd921a8835092a..f35fa93c762f361e1c4db4a1f597952b3f927fd0 100755
--- a/reviewboard/cmdline/rbsite.py
+++ b/reviewboard/cmdline/rbsite.py
@@ -1174,7 +1174,12 @@ class Site(object):
         url = get_register_support_url(force_is_admin=True)
 
         try:
-            urlopen(url, timeout=5).read()
+            from reviewboard.certs import cert_manager
+            urlopen(
+                url,
+                timeout=5,
+                **cert_manager.build_urlopen_kwargs(url=url),
+            ).read()
         except Exception:
             # There may be a number of issues preventing this from working,
             # such as a restricted network environment or a server issue on
diff --git a/reviewboard/notifications/webhooks.py b/reviewboard/notifications/webhooks.py
index 35e1a8691a12e84e0f8d95d23c874f61f170ba97..b4e021d33378e3a7fe42b6530867a835bc34b9d2 100644
--- a/reviewboard/notifications/webhooks.py
+++ b/reviewboard/notifications/webhooks.py
@@ -8,6 +8,7 @@ import logging
 from base64 import b64encode
 from collections import OrderedDict
 from datetime import datetime
+from typing import TYPE_CHECKING
 from urllib.error import HTTPError
 from urllib.parse import urlencode, urlsplit, urlunsplit
 from urllib.request import Request, urlopen
@@ -29,6 +30,7 @@ from djblets.webapi.encoders import (BasicAPIEncoder, JSONEncoderAdapter,
                                      ResourceAPIEncoder, XMLEncoderAdapter)
 
 from reviewboard import get_package_version
+from reviewboard.certs.manager import cert_manager
 from reviewboard.notifications.models import WebHookTarget
 from reviewboard.reviews.models import Review, ReviewRequest
 from reviewboard.reviews.signals import (review_request_closed,
@@ -37,6 +39,11 @@ from reviewboard.reviews.signals import (review_request_closed,
                                          review_published,
                                          reply_published)
 
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+    from typelets.json import JSONDict
+
 
 logger = logging.getLogger(__name__)
 
@@ -277,7 +284,12 @@ def normalize_webhook_payload(payload, request, use_string_keys=False):
     return _normalize_value(payload)
 
 
-def dispatch_webhook_event(request, webhook_targets, event, payload):
+def dispatch_webhook_event(
+    request: HttpRequest,
+    webhook_targets: Sequence[WebHookTarget],
+    event: str,
+    payload: JSONDict,
+) -> None:
     """Dispatch the given event and payload to the given WebHook targets.
 
     Args:
@@ -289,7 +301,7 @@ def dispatch_webhook_event(request, webhook_targets, event, payload):
             The list of WebHook targets containing endpoint URLs to dispatch
             to.
 
-        event (unicode):
+        event (str):
             The name of the event being dispatched.
 
         payload (dict):
@@ -417,7 +429,13 @@ def dispatch_webhook_event(request, webhook_targets, event, payload):
                     headers['Authorization'] = \
                         'Basic %s' % b64encode(credentials.encode('utf-8'))
 
-                urlopen(Request(url, body, headers))
+                urlopen(
+                    Request(url, body, headers),
+                    **cert_manager.build_urlopen_kwargs(
+                        url=url,
+                        local_site=webhook_target.local_site,
+                    ),
+                )
             except Exception as e:
                 logger.exception('[%s] Could not dispatch WebHook to %s: %s',
                                  log_timer.trace_id, webhook_target.url, e,
diff --git a/reviewboard/scmtools/core.py b/reviewboard/scmtools/core.py
index 12b696eb543704478b0b8bbb9bfab6c3e28f3638..e26254b9e23e45c27548fc22eff1ebda924676f8 100644
--- a/reviewboard/scmtools/core.py
+++ b/reviewboard/scmtools/core.py
@@ -20,6 +20,7 @@ from djblets.log import log_timed
 from djblets.util.properties import TypedProperty
 from typing_extensions import TypeAlias
 
+from reviewboard.certs.manager import cert_manager
 from reviewboard.scmtools.errors import (AuthenticationError,
                                          FileNotFoundError,
                                          SCMError)
@@ -1820,7 +1821,13 @@ class SCMClient:
                     request.add_header('Authorization',
                                        f'Basic {auth_string}')
 
-                response = urlopen(request)
+                response = urlopen(
+                    request,
+                    **cert_manager.build_urlopen_kwargs(
+                        url=url,
+                        local_site=self.local_site,
+                    ),
+                )
 
                 if (mime_type is None or
                     response.info()['Content-Type'] == mime_type):