fixup! Allow the application to configure Turbo::StreamChannel’s inhe…

…ritance

`ApplicationCable::Connection` allows the application to apply
authentication to all streams method, including those from
`Turbo::Broadcastable`.

By allowing `Turbo::StreamsChannel` to inherit from
`ApplicationCable::Channel` we open up a symmetrical path for
authorization.

In the spirit of being secure by default we should be moving towards
making `Turbo.base_stream_channel_class` default to
`"ApplicationCable::Channel"` but doing so without warning would break
applications relying on `ApplicationCable::Connection#authorized?` for
non-turbo broadcastable streams only.

Once we deem it safe we can remove the awkward initialiser and hard code
`ApplicationCable::Channel` as the super class. If people needs
different super classes for `Turbo::StreamsChannel` and custom channels
they can simply add another super class to inherit from in their
application.

test/streams/streams_channel_test.rb

@@ -346,28 +346,32 @@ class Turbo::StreamsChannelTest < ActionCable::Channel::TestCase
   end
 
   test "confirms subscription when succeeding authorization" do
-    board = Board.create!(name: "A")
-    original_authorized = Turbo::StreamsChannel.instance_method(:authorized?)
-    Turbo::StreamsChannel.define_method(:authorized?) { streamable.name == "A" }
+    authorizing do |record|
+      Turbo::StreamsChannel.define_method(:authorized?) { streamable.name == record.name }
+      subscribe signed_stream_name: signed_stream_name(record)
 
-    subscribe signed_stream_name: signed_stream_name(board)
-
-    assert subscription.confirmed?
-    assert_has_stream board.to_gid_param
-  ensure
-    Turbo::StreamsChannel.define_method :authorized?, original_authorized
+      assert subscription.confirmed?
+      assert_has_stream record.to_gid_param
+    end
   end
 
   test "rejects subscription when failing authorization" do
-    board = Board.create!(name: "A")
-    original_authorized = Turbo::StreamsChannel.instance_method(:authorized?)
-    Turbo::StreamsChannel.define_method(:authorized?) { streamable.name == "B" }
-
-    subscribe signed_stream_name: signed_stream_name(board)
+    authorizing do |record|
+      Turbo::StreamsChannel.define_method(:authorized?) { streamable.name != record.name }
+      subscribe signed_stream_name: signed_stream_name(record)
 
-    assert subscription.rejected?
-    assert_no_streams
-  ensure
-    Turbo::StreamsChannel.define_method :authorized?, original_authorized
+      assert subscription.rejected?
+      assert_no_streams
+    end
   end
+
+  private
+    def authorizing
+      record = Board.create!(name: "Some name")
+      original_authorized = Turbo::StreamsChannel.instance_method(:authorized?)
+      yield record
+    ensure
+      Turbo::StreamsChannel.define_method :authorized?, original_authorized
+      record.destroy
+    end
 end