diff --git a/app/__init__.py b/app/__init__.py
index 7669fbc73..48a664431 100644
--- a/app/__init__.py
+++ b/app/__init__.py
@@ -38,7 +38,6 @@ from werkzeug.local import LocalProxy
 from app import proxy_fix
 from app.config import configs
 from app.asset_fingerprinter import AssetFingerprinter
-from app.its_dangerous_session import ItsdangerousSessionInterface
 from app.notify_client.service_api_client import ServiceAPIClient
 from app.notify_client.api_key_api_client import ApiKeyApiClient
 from app.notify_client.invite_api_client import InviteApiClient
@@ -124,8 +123,6 @@ def create_app(application):
 
     proxy_fix.init_app(application)
 
-    application.session_interface = ItsdangerousSessionInterface()
-
     add_template_filters(application)
 
     register_errorhandlers(application)
@@ -139,6 +136,16 @@ def init_app(application):
     application.before_request(load_service_before_request)
     application.before_request(request_helper.check_proxy_header_before_request)
 
+    @application.before_request
+    def make_session_permanent():
+        # this is dumb. You'd think, given that there's `config['PERMANENT_SESSION_LIFETIME']`, that you'd enable
+        # permanent sessions in the config too - but no, you have to declare it for each request.
+        # https://stackoverflow.com/questions/34118093/flask-permanent-session-where-to-define-them
+        # session.permanent is also, helpfully, a way of saying that the session isn't permanent - in that, it will
+        # expire on its own, as opposed to being controlled by the browser's session. Because session is a proxy, it's
+        # only accessible from within a request context, so we need to set this before every request :rolls_eyes:
+        session.permanent = True
+
     @application.context_processor
     def _attach_current_service():
         return {'current_service': current_service}
diff --git a/app/its_dangerous_session.py b/app/its_dangerous_session.py
deleted file mode 100644
index e16cecc55..000000000
--- a/app/its_dangerous_session.py
+++ /dev/null
@@ -1,53 +0,0 @@
-from datetime import timedelta, datetime
-
-from werkzeug.datastructures import CallbackDict
-from flask.sessions import SessionInterface, SessionMixin
-from itsdangerous import URLSafeTimedSerializer, BadSignature
-
-
-class ItsdangerousSession(CallbackDict, SessionMixin):
-    def __init__(self, initial=None):
-        def on_update(self):
-            self.modified = True
-
-        CallbackDict.__init__(self, initial, on_update)
-        self.modified = False
-
-
-class ItsdangerousSessionInterface(SessionInterface):
-    session_class = ItsdangerousSession
-
-    def get_serializer(self, app):
-        salt = app.config.get('DANGEROUS_SALT')
-        if not app.secret_key:
-            return None
-        return URLSafeTimedSerializer(app.secret_key,
-                                      salt=salt)
-
-    def open_session(self, app, request):
-        s = self.get_serializer(app)
-        if s is None:
-            return None
-        val = request.cookies.get(app.session_cookie_name)
-        if not val:
-            return self.session_class()
-        max_age = app.permanent_session_lifetime.total_seconds()
-        try:
-            data = s.loads(val, max_age=max_age)
-            return self.session_class(data)
-        except BadSignature:
-            return self.session_class()
-
-    def save_session(self, app, session, response):
-        domain = self.get_cookie_domain(app)
-        if not session:
-            if session.modified:
-                response.delete_cookie(app.session_cookie_name,
-                                       domain=domain)
-            return
-        session.permanent = True
-        expires = datetime.utcnow() + timedelta(seconds=app.config.get('PERMANENT_SESSION_LIFETIME'))
-        val = self.get_serializer(app).dumps(dict(session))
-        response.set_cookie(app.session_cookie_name, val,
-                            expires=expires, httponly=True,
-                            domain=domain, secure=app.config.get('SESSION_COOKIE_SECURE'))