Add ci.opensearch.org/m2/ mirror for plugin resolution (custom-codecs)

[shreyah963]

Description

Add ci.opensearch.org/m2/ mirror for plugin resolution (custom-codecs)

Issues Resolved

opensearch-project/opensearch-build#6278 (comment)

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[github-actions]

PR Code Analyzer ❗

AI-powered 'Code-Diff-Analyzer' found issues on commit b87e26d.

⛔ Hard block: Issues at High severity or above will block this PR from merging.

Path	Line	Severity	Description
build.gradle	41	high	New Maven repository source added: https://ci.opensearch.org/m2/ in buildscript block. Per mandatory rule, all package registry changes must be flagged — artifact authenticity cannot be verified and this path differs from the pre-existing /maven2/ path on the same host.
build.gradle	69	high	New Maven repository source added: https://ci.opensearch.org/m2/ in main repositories block. Same unverified path as buildscript addition; artifacts resolved from this repo could be substituted for legitimate dependencies.
bwc-test/build.gradle	53	high	New Maven repository source added: https://ci.opensearch.org/m2/ in buildscript repositories block. Mandatory flag: unverifiable repository source added alongside existing /maven2/ path — could serve different or malicious artifacts.
bwc-test/build.gradle	67	high	New Maven repository source added: https://ci.opensearch.org/m2/ in main repositories block. Mandatory flag: same unverified path; build tooling resolves dependencies in declaration order, so priority relative to other repos should be audited.
settings.gradle	11	high	New Maven repository source added: https://ci.opensearch.org/m2/ in pluginManagement block. Mandatory flag: plugin management repositories control Gradle plugin resolution — a malicious artifact served from this path could execute arbitrary code during the build.

The table above displays the top 10 most important findings.

Total: 5 | Critical: 0 | High: 5 | Medium: 0 | Low: 0

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Pull Requests Author(s): Please update your Pull Request according to the report above.

Repository Maintainer(s): You can bypass diff analyzer by adding label skip-diff-analyzer after reviewing the changes carefully, then re-run failed actions. To re-enable the analyzer, remove the label, then re-run all actions.

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⚠️ Note: The Code-Diff-Analyzer helps protect against potentially harmful code patterns. Please ensure you have thoroughly reviewed the changes beforehand.

Thanks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@7851ab3). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #359   +/-   ##
=======================================
  Coverage        ?   48.88%           
  Complexity      ?      192           
=======================================
  Files           ?       54           
  Lines           ?     1162           
  Branches        ?       64           
=======================================
  Hits            ?      568           
  Misses          ?      558           
  Partials        ?       36           

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