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  • License MIT

OpenAI ChatGPT (Codex backend) OAuth auth plugin for opencode - use your ChatGPT Plus/Pro subscription instead of API credits

Package Exports

  • opencode-openai-codex-auth
  • opencode-openai-codex-auth/index.mjs

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (opencode-openai-codex-auth) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

OpenAI ChatGPT OAuth Plugin for opencode

This plugin enables opencode to use OpenAI's Codex backend via ChatGPT Plus/Pro OAuth authentication, allowing you to use your ChatGPT subscription instead of OpenAI Platform API credits.

Features

  • ✅ ChatGPT Plus/Pro OAuth authentication
  • ✅ Zero external dependencies - Lightweight with only @openauthjs/openauth
  • ✅ Auto-refreshing tokens - Handles token expiration automatically
  • ✅ Auto-updating Codex instructions - Fetches latest from OpenAI's Codex repo (cached 24h)
  • ✅ Full tool support (write, edit, bash, grep, etc.)
  • ✅ Automatic tool remapping (Codex tools → opencode tools)
  • ✅ High reasoning effort with detailed thinking blocks
  • ✅ Modular architecture for easy maintenance

Installation

npm install opencode-openai-codex-auth

Add the plugin to your opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": [
    "opencode-openai-codex-auth"
  ],
  "model": "openai/gpt-5-codex"
}

From source

  1. Clone this repository:
git clone https://github.com/numman/opencode-openai-codex-auth.git
cd opencode-openai-codex-auth
npm install
  1. Add the plugin to your opencode.json:
{
  "$schema": "https://opencode.ai/config.json",
  "plugin": [
    "file:///absolute/path/to/opencode-openai-codex-auth"
  ],
  "model": "openai/gpt-5-codex"
}

Authentication

Login with ChatGPT OAuth:

opencode auth login

Select "OpenAI" and choose:

  • "ChatGPT Plus/Pro (Codex Subscription)" - Opens browser automatically for OAuth flow

Important: Make sure the official Codex CLI is not running during first login, as both use port 1455 for OAuth callback. After initial authentication, this won't be an issue.

Usage

# Use gpt-5-codex with high reasoning (default)
opencode run "create a hello world file" --model=openai/gpt-5-codex

# Or set as default in opencode.json
opencode run "solve this complex algorithm problem"

The plugin automatically configures:

  • High reasoning effort for deep thinking
  • Detailed reasoning summaries to show thought process
  • Medium text verbosity for balanced output

How It Works

The plugin:

  1. Authentication: Uses ChatGPT OAuth flow with PKCE for secure authentication
  2. Token Management: Auto-refreshes tokens using ai-sdk-provider-chatgpt-oauth
  3. Codex Instructions: Automatically fetches latest instructions from openai/codex repository
    • Cached locally in ~/.opencode/cache/ for 24 hours
    • Falls back to bundled version if GitHub is unavailable
  4. Request Transformation: Routes requests to https://chatgpt.com/backend-api/codex/responses
  5. Model Normalization: Maps all model names to gpt-5-codex (the Codex backend model)
  6. Tool Remapping: Injects instructions to map Codex tools to opencode tools:
    • apply_patch → edit
    • update_plan → todowrite
  7. Reasoning Configuration: Forces high reasoning effort with detailed summaries
  8. History Filtering: Removes stored conversation IDs since Codex uses store: false

Limitations

  • ChatGPT Plus/Pro required: Must have an active ChatGPT Plus or Pro subscription
  • Medium text verbosity: Codex only supports medium for text verbosity

Troubleshooting

Authentication Issues

  • Ensure you have an active ChatGPT Plus or Pro subscription
  • Try re-logging in with opencode auth login
  • Check browser console during OAuth flow if auto-login fails

Tool Execution Issues

  • Verify plugin is loaded in opencode.json
  • Check that model is set to openai/gpt-5-codex
  • Check ~/.opencode/cache/ for cached instructions (auto-downloads from GitHub)

Request Errors

  • 401 Unauthorized: Token expired, run opencode auth login again
  • 400 Bad Request: Check console output for specific error details
  • 403 Forbidden: Subscription may be expired or invalid

Project Structure

opencode-openai-codex-auth/
├── index.mjs              # Main plugin entry point
├── lib/
│   ├── auth.mjs          # OAuth authentication logic
│   ├── codex.mjs         # Codex instructions & tool remapping
│   ├── server.mjs        # Local OAuth callback server
│   └── codex-instructions.md  # Bundled Codex instructions (fallback)
├── package.json
├── README.md
└── LICENSE

Module Overview

  • index.mjs: Main plugin export and request transformation
  • lib/auth.mjs: OAuth flow, PKCE, token exchange, JWT decoding
  • lib/codex.mjs: Fetches/caches Codex instructions from GitHub, tool remapping
  • lib/server.mjs: Local HTTP server for OAuth callback handling

Credits

Based on research and working implementations from:

License

MIT