[Feature] Add signature validation

[mkohei]

WHY are these changes introduced?

Because there is no Signature verification when using app proxy.

WHAT is this pull request doing?

Add Utils::validateSignature($params, $secret)

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have updated the documentation for public APIs from the library (if applicable)

[sebastianpisula]

great idea! It still works?

[wardwj]

Can we get this added? PR is still valid and works