[Bug]: Signatures - Passing extra data not typed is added in the signature but not visible on the UI

[seaona]

Describe the bug

Problem: passing extra data which is not in the typed definition, results in being it hidden in the UI but actually being signed in the signature result

Expected behavior

No response

Screenshots/Recordings

metamask-signature-type-obfuscated.mp4

Steps to reproduce

(See video)

1. Checkout test-dapp
2. Add an extra field in a typed 4 signature
3. Sign it -- see the extra data is not there
4. Copy the hash result
5. Remove the extra field in the same signature
6. Sign it -- copy the hash result
7. Compare to hashes -- see they are different

Error messages or log output

No response

Version

11.9.0 but introduced earlier

Build type

None

Browser

Chrome

Operating system

Linux

Hardware wallet

No response

Additional context

No response

Severity

No response

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity in the last 90 days. It will be closed in 45 days if there is no further activity. The MetaMask team intends on reviewing this issue before close, and removing the stale label if it is still a bug. We welcome new comments on this issue. We do not intend on closing issues if they report bugs that are still reproducible. Thank you for your contributions.

[jpuri]

This is as per requirement, please check this PR: MetaMask/metamask-mobile#9795

Fields which are not typed are not part of finally signed message.