Remove push subscriptions on a password change, and post them again

A push subscription belongs to the user, not a session, so a device
signed out by a password change kept getting notifications. Changing
the password now removes every subscription along with the sessions,
in the same transaction.

A browser still signed in keeps its own subscription in its service
worker, so the notifications controller posts it once per session: the
bell names the session by a digest of its id, never its token, and the
browser remembers the last one it posted for. That post never
unsubscribes the browser when the server refuses it.

A request that authenticated just before the change could put a
subscription back after it. The create action now checks the session
still exists and saves in one immediate transaction, after validating
the endpoint outside it.

From #371.

(cherry picked from commit 6cab924097)

test/system/push_subscription_resync_test.rb

@@ -0,0 +1,71 @@
+require "application_system_test_case"
+
+class PushSubscriptionResyncTest < ApplicationSystemTestCase
+  ENDPOINT = "https://fcm.googleapis.com/fcm/send/system-test"
+
+  setup do
+    stub_web_push_dns_resolution
+    fake_a_browser_push_subscription
+  end
+
+  teardown do
+    page.execute_script("localStorage.clear()") if page.current_url.start_with?("http")
+  end
+
+  test "a browser posts its subscription again once per session, so it survives a password change" do
+    sign_in "david@37signals.com"
+    assert_subscription_registered
+    first_sync = subscription.updated_at
+
+    join_room rooms(:hq)
+    assert_equal first_sync, subscription.reload.updated_at, "posted again in the same session"
+
+    change_password
+    assert_nil Push::Subscription.find_by(endpoint: ENDPOINT)
+
+    join_room rooms(:hq)
+    assert_subscription_registered
+    assert_not page.evaluate_script("localStorage.getItem('unsubscribed-for-test')")
+  end
+
+  test "a subscription the server refuses stays in the browser" do
+    stub_dns_resolution("169.254.169.254")
+
+    sign_in "david@37signals.com"
+    Timeout.timeout(5) { sleep 0.1 until page.evaluate_script("localStorage.getItem('push-subscription-synced-session')") }
+    join_room rooms(:hq)
+
+    assert_not Push::Subscription.exists?(endpoint: ENDPOINT)
+    assert_not page.evaluate_script("localStorage.getItem('unsubscribed-for-test')")
+  end
+
+  private
+    # Headless Chrome has no push service, so stand in for the subscription the service worker would hold.
+    def fake_a_browser_push_subscription
+      page.driver.browser.execute_cdp "Page.addScriptToEvaluateOnNewDocument", source: <<~JS
+        Object.defineProperty(Notification, "permission", { get: () => "granted" })
+        const subscription = {
+          toJSON: () => ({ endpoint: "#{ENDPOINT}", keys: { p256dh: "p256dh-key", auth: "auth-key" } }),
+          unsubscribe: async () => { localStorage.setItem("unsubscribed-for-test", "true") }
+        }
+        navigator.serviceWorker.getRegistration = async () => ({ pushManager: { getSubscription: async () => subscription } })
+      JS
+    end
+
+    def change_password
+      visit user_profile_url
+      find("input[name='user[password_challenge]']").fill_in with: "secret123456"
+      find("input[name='user[password]']").fill_in with: "a new secret123456"
+      find("input[name='user[password]']").send_keys :enter
+      assert_selector ".flash", text: "✓"
+    end
+
+    def assert_subscription_registered
+      assert_selector "[data-controller~=notifications]", visible: :all
+      Timeout.timeout(5) { sleep 0.1 until Push::Subscription.exists?(endpoint: ENDPOINT, user: users(:david)) }
+    end
+
+    def subscription
+      Push::Subscription.find_by!(endpoint: ENDPOINT)
+    end
+end