[FUNK-2000] Fixed extensible webhook shared secret issue

[vaibhav-nanda]

https://twilio-engineering.atlassian.net/browse/FUNK-2000
The X-Signature is not being sent for extensible webhook right now, although the UI provides an option to add the sharedSecret just like webhooks destination.

Testing

This is tested in staging. The shared secret val is being used to send the required data in x-signature header.

• Added unit tests for new functionality
• Tested end-to-end using the local server
• [If destination is already live] Tested for backward compatibility of destination. Note: New required fields are a breaking change.
• [Segmenters] Tested in the staging environment
• [Segmenters] [If applicable for this change] Tested for regression with Hadron.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.03%. Comparing base (7710428) to head (d0e3291).

Files with missing lines	Patch %	Lines
...tions/src/destinations/webhook-extensible/index.ts	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3316   +/-   ##
=======================================
  Coverage   80.03%   80.03%           
=======================================
  Files        1202     1202           
  Lines       22105    22112    +7     
  Branches     4355     4359    +4     
=======================================
+ Hits        17691    17697    +6     
  Misses       3637     3637           
- Partials      777      778    +1     

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[joe-ayoub-segment]

Hi @vaibhav-nanda ping me here when you need this reviewed.

[joe-ayoub-segment]

Hi @vaibhav-nanda I have a few questions about this:

1. Do we need the xSignatureHeader to always be present if the customer provides a sharedSecret?

2. How do you know that you are generating the xSignatureHeader correctly?

3. This Action implements the performBatch() function. If we send a batch of events then I assume the xSignatureHeader needs to created based off of all the data being sent - is that correct?

4. Shouldn't the xSignatureHeader value be generated from the actual payload being sent to the destination platform, rather than the input payload values? I can see that the data object gets encoded before it gets sent. if (data) return encodeBody(data, contentType)