Upgrade JJWT to 0.12.6 and update JwtService for compatibility

[reetikg]

Issue number: resolves #372

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Checklist

• [yes ] Code Formatter (run prettier/spotlessApply)
• [ no] Code has unit tests? (Existing tests cover JwtService)
• [ yes] Builds on localhost
• [yes ] Builds/Runs in docker compose

What is the current behavior?

The project uses JJWT 0.11.5, which allows JWT signing with an RSA key using older, now-deprecated methods. It does not enforce explicit use of cryptographic key types, leading to weaker security and incompatibility with newer JJWT versions.

What is the new behavior?

->Updated JJWT dependencies to version 0.12.6 in server/build.gradle.

->Refactored JwtService:

    JWT signing now uses Jwts.builder().signWith(RsaSigner).

    JWT verification now uses Jwts.parser().verifyWith(RsaVerifier).

->Introduced use of the public RSA key explicitly with verifyWith(pubKey) to validate JWTs in compliance with JJWT 0.12.6.

->Ensures cryptographically sound JWT creation and validation, enforcing best practices and improving library compatibility.

->All tests pass successfully and the application builds and runs locally and in Docker.

Does this introduce a breaking change?

• [ ✓ ] Yes
• No

1.JWT consumers (any service or client verifying tokens) must update their logic to use the RSA public key to validate tokens.

2.The signing and verification process now uses the updated JJWT 0.12.6 API, which requires explicit key handling (RsaSigner for signing, verifyWith(pubKey) for verification).

3.Any system that relies on decoding or verifying JWTs (e.g., mobile apps, other backend services) must ensure:

      They use a compatible JWT library.

      They verify tokens using the provided RSA public key.

4.The token structure/signature may differ slightly under the new signing method — if consumers parse JWTs manually, validation may fail unless updated.

Other information

[R-Sandor]

@reetikg Thanks for the PR, I am going to review this shortly. Just wanted you to see I did see :)

[R-Sandor]

Thank you 🚀
I pulled everything locally to confirm. Everything is working.