feat(webhook-callbacks): add support for verifying http request signatures

[hamzamahmood]

Why

To ensure secure handling of incoming webhook and callback requests, we need to validate their authenticity. Without signature verification, there is a risk of processing spoofed or tampered requests. Adding a standard verification mechanism also makes it easier to plug in custom verification strategies as needed.

What

• IHttpRequstData interface added to handle asp.net and asp.netcore requests
• Introduced ISignatureVerifier contract to enable pluggable custom verification implementations.
• Added configurable HMAC signature verification as the default implementation.
• Implemented DigestCodec with support for Hex, Base64, and Base64Url encodings.
• Added unit tests to validate the correctness of signature verification.

Type of change

Select multiple if applicable.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause a breaking change)
• Tests (adds or updates tests)
• Documentation (adds or updates documentation)
• Refactor (style improvements, performance improvements, code refactoring)
• Revert (reverts a commit)
• CI/Build (adds or updates a script, change in external dependencies)

Testing

Unit tests for the signature verification have been added

Checklist

• My code follows the coding conventions
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added new unit tests