fix: marketplace add authenticates for private repos

[jacobokeeffe-ow]

Description

Fix apm marketplace add failing to fetch marketplace.json from private repositories, even when valid authentication tokens are available.

Fixes #669

Type of change

• Bug fix
• New feature
• Documentation
• Maintenance / refactor

Root cause

_do_fetch() in client.py returned None on HTTP 404 regardless of whether a token was present. Since try_with_fallback(unauth_first=True) only escalates to authenticated retry on exceptions (not None returns), the auth fallback never fired for private repos. GitHub returns 404 (not 403) for private repos to avoid leaking existence, making the unauthenticated 404 indistinguishable from "file not found."

Fix

When _do_fetch() receives a 404 without a token, it now raises via resp.raise_for_status() so that try_with_fallback catches the exception and retries with authentication. When a 404 is received with a token, it still returns None (the file genuinely doesn't exist).

This preserves the rate-limit optimization for public repos (unauthenticated requests succeed on first try) while correctly handling private repos.

Testing

• Tested locally
• All existing tests pass (3827 passed)
• Added tests for new functionality (if applicable)

4 new tests in TestPrivateRepoAuth:

• test_private_repo_unauthenticated_404_retries_with_token — core regression test
• test_authenticated_404_returns_none — genuinely missing files still return None
• test_public_repo_unauthenticated_success — no regression for public repos
• test_auto_detect_private_repo_finds_marketplace_json — end-to-end through _auto_detect_path

Also verified against a real private marketplace repo — the fix correctly resolves marketplace.json and returns both plugins.

[jacobokeeffe-ow]

@microsoft-github-policy-service agree company="Oliver Wyman"

[jacobokeeffe-ow]

@sergio-sisternes-epam apologies for the formatting changes but when I run uv run black . I end up with 308 files reformatted. I followed the instructions in the contributing guide and don't see anything obvious I'm doing wrong.

I might be mistaken but I don't see black being run as part of CI so I'm wondering if the whole repo genuinely needs reformatting or if maybe the instructions just need updating - let me know!

[sergio-sisternes-epam]

Clean fix -- the 6-line change in _do_fetch() correctly distinguishes "private repo hiding existence" from "file not found" by raising on unauthenticated 404 to trigger try_with_fallback auth retry. Good test coverage with 4 regression tests.

Re: formatting -- we don't enforce black in CI, so the reformatting here is fine (contained to files you touched). We should update the contributing guide to clarify this. Thanks for flagging it!

Note: CI hasn't run yet (fork PR). Would be good to get Build & Test triggered before merge.

[jacobokeeffe-ow]

thanks @sergio-sisternes-epam.

I think you might need to give approval in order the get the github action to run? https://github.com/microsoft/apm/actions/runs/24339327316 : "This workflow is awaiting approval from a maintainer"