How to configure auth service for signup confirmation email and PostConfirmation trigger in headless mode?

**Which Category is your question related to?**
Amplify Auth Headless provisioning

**Amplify CLI Version**
7.6.4

**What AWS Services are you utilizing?**
Amplify

**Provide additional details e.g. code snippets**
I am provisioning amplify through headless mechanism for CI/CD as per this document [Headless mode for CI/CD](https://docs.amplify.aws/cli/usage/headless/).

I am able to initialize amplify, add api, add auth and push using headless method. However, I do not find any properties in "add auth" JSON payload to setup PostConfirmation Lambda trigger. Any help on how to achieve this is appreciated.

Thanks.

Start with the linked Headless mode for CI/CD documentation and the Amplify CLI add-auth JSON payload described in the issue. Determine whether PostConfirmation and signup-confirmation settings are supported in headless provisioning; done means documenting the supported configuration or the limitation and its workaround.

Written by the indexing model from the issue text.