CORS for operation type subscription

I am working on an app using AWS AppSync. I have enabled the AuthN and AuthZ.

One part I am stuck is at adding CORS filter for Appsync subscriptions.

I have worked on websockets earlier and there too I had this problem. I solved it manually in websockets by filtering the CORS from header during the handshake.

Do we have a provision to invoke a lambda in Appsync when a client is attempting to connect for subscription ?

I have also posted this exact question in Stackoverflow.
https://stackoverflow.com/questions/64520754/add-cors-filter-in-appsync-subscription

Start with the AWS AppSync subscription connection and CORS behavior described in the issue, then compare it with the linked Stack Overflow question. Done means establishing whether a Lambda can be invoked when a subscription client connects and documenting the supported way to handle CORS, if one exists.

Written by the indexing model from the issue text.