Fix intermittent token service test failures caused by Base64 padding

[Copilot]

Summary

Two token verification tests were failing intermittently (~4% of runs) because they modified the last character of JWT tokens. Due to Base64 URL-safe encoding with 43-character signatures, the last character only contributes 2 bits to the decoded value. Characters 'U' and 'X' share the same high-order 4 bits (010100 vs 010111), so modifying 'U'→'X' produces an identical decoded signature, correctly passing verification.

Changes:

• Modified tests to change middle characters instead of trailing characters, ensuring decoded values always differ
• Added constants MIN_TOKEN_LENGTH_FOR_MODIFICATION and MIN_SIGNATURE_LENGTH_FOR_MODIFICATION
• Added explanatory comments about the Base64 padding edge case

Example of the issue:

# Base64 decode shows why 'U' and 'X' are equivalent:
sig = "NSTtSO04ZCh7kcmvXDxjm5vuLW_6a8GBDXKWtm_H0UU"
sig_modified = "NSTtSO04ZCh7kcmvXDxjm5vuLW_6a8GBDXKWtm_H0UX"
# Both decode to: 3524ed48ed3864287b91c9af5c3c639b9bee2d6ffa6bc1810d7296b66fc7d145

Related Issues / Discussions

Issue describes the intermittent test failures with full error logs.

QA Instructions

Run the affected tests multiple times to verify deterministic behavior:

for i in {1..20}; do python -m pytest tests/app/services/auth/test_token_service.py::TestTokenVerification::test_verify_token_with_modified_payload tests/app/services/auth/test_token_service.py::TestTokenSecurity::test_token_signature_verification -q; done

All runs should pass. Previously, approximately 4% would fail.

Merge Plan

N/A - Test-only changes, no production code affected.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[bug]: Token service test failures</issue_title>
<issue_description>### Is there an existing issue for this problem?

• I have searched the existing issues

Install method

Invoke's Launcher

Operating system

Linux

GPU vendor

Nvidia (CUDA)

GPU model

No response

GPU VRAM

No response

Version number

lstein-master HEAD

Browser

No response

System Information

No response

What happened

Two unit tests in tests/app/services/auth/test_token_service.py are intermittently failing:

1. test_verify_token_with_modified_payload()
2. test_token_signature_verification()

Here is the short test summary info. The full error log is attached.

=========================== short test summary info ============================
206
FAILED tests/app/services/auth/test_token_service.py::TestTokenVerification::test_verify_token_with_modified_payload - AssertionError: assert TokenData(user_id='user123', email='test@example.com', is_admin=False) is None
207
FAILED tests/app/services/auth/test_token_service.py::TestTokenSecurity::test_token_signature_verification - AssertionError: assert TokenData(user_id='user123', email='test@example.com', is_admin=False) is None
208
 +  where TokenData(user_id='user123', email='test@example.com', is_admin=False) = verify_token('***')
209
= 2 failed, 783 passed, 102 skipped, 4 deselected, 8 warnings in 206.16s (0:03:26) =
210
Error: Process completed with exit code 1.

test.txt

What you expected to happen

I expect the auth unit tests to succeed.

How to reproduce the problem

No response

Additional context

No response

Discord username

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [bug]: Token service test failures #31

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