Introduce a custom AsyncAPI extension to incorporate signature verification for webhook payloads

[chathushkaayash]

Description

When addressing the issue providing a way to configure the HTTP Listener configurations in the AsyncAPI-generated listeners, we need to consider additional fields that can be included in ListenerConfiguration. Typically, this includes tokens related to webhook signature verification.

Problem Statement

In the ListenerConfiguration of the Ballerina asyncapi-triggers, certain fields are typically required to handle webhook signature verification. These fields often include secrets or tokens used for verifying incoming webhook requests. However, the current Ballerina service and listener skeleton generation process does not allow us to specify these tokens or the verification process in the AsyncAPI specification.

Current Workaround

Since there is no way to define these additional configurations in the generated listener, we currently:

• Manually extend the ListenerConfiguration to include the necessary tokens.
• Implement the signature verification logic manually within the generated service.

Proposed Solution

To make webhook signature verification more seamless, we should introduce a way to define these additional configurations directly in the AsyncAPI specification. One potential approach is to utilize custom extensions in the AsyncAPI spec to define signature verification tokens and have them reflected in the generated Ballerina listener.