[WIP] Create workflow to bill Codex subscription instead of API key

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create a workflow that bills the Codex subscription instead of API key</issue_title>
<issue_description>How to create a workflow such that it bills against a Codex monthly subscription (e.g. chatgpt plus or pro) instead of a codex API key?</issue_description>

<agent_instructions> This mirrors how Claude already supports dual auth (ANTHROPIC_API_KEY + CLAUDE_CODE_OAUTH_TOKEN).

Approach

Add a new secret CODEX_CHATGPT_REFRESH_TOKEN. When provided, the workflow writes ~/.codex/auth.json with the ChatGPT auth mode and unsets the API key env vars so Codex uses subscription billing instead.</agent_instructions>

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

@pelikhan Please do a deep research on this topic including docs and integration guides. @Mossaka Let me take a look at this issue @Mossaka It looks like we need to support a new environment variable `CODEX_CHATGPT_REFRESH_TOKEN.` so Codex uses subscription billing instead

Custom agent used: developer.instructions
Developer Instructions for GitHub Agentic Workflows

• Fixes Create a workflow that bills the Codex subscription instead of API key #15510

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