[Security] Implement Notification Payload Integrity Verification

[Abd-Standard]

Description

Strengthen notification security by verifying payload integrity before processing. The verification mechanism should detect tampered payloads and reject invalid requests before they enter the processing pipeline.

Tasks
Generate payload integrity hashes.
Validate hashes during processing.
Reject tampered payloads.
Log integrity verification failures.
Add unit and integration tests.

Acceptance Criteria
Payload integrity is verified successfully.
Modified payloads are rejected.
Verification failures are logged.
Test coverage includes valid and tampered payload scenarios.

Contributors start work by running:
git checkout -b security/payload-integrity-verification

[Ebenezer199914]

can i work on this issue

[AbuJulaybeeb]

Hi Maintainer, haven reviewed the description of the issue, and well experienced with Js Library,
I would like to hop on the issue and sure to deliver at ETA 2hrs

[ghost-cy829]

I would like to work on this issue. I have experience with Rust and Soroban smart contract development. I will follow the acceptance criteria and add tests. Excited to contribute. Kindly assign.

[aetheron06]

I’m interested in tackling this! I have a strong background in smart contract development and full-stack systems, so I'm well-equipped to handle the requirements here. Could you please assign this to me?

[michaelvic123]

Hi! I'd like to work on this issue. It aligns with my experience, and I'm confident I can deliver a well-tested solution. Could you please assign it to me? Thanks!

[grantfox-oss]

🦊 GrantFox — @michaelvic123 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #355)
2. Your PR will be reviewed by the Core-Foundry maintainers

Good luck! Track your progress on GrantFox.