v1.0.0: Production-ready OpenAI Codex OAuth plugin

Features:
- ChatGPT Plus/Pro OAuth authentication with auto-refresh
- Auto-updating Codex instructions from GitHub (24h cache)
- Zero dependencies except @openauthjs/openauth
- Modular architecture (auth, codex, server modules)
- Full tool support with automatic remapping
- High reasoning effort with detailed thinking blocks

Package size: 13.5 kB compressed, 36.7 kB unpacked

Author: Numman Ali

.gitignore

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+node_modules/
+bun.lockb
+pnpm-lock.yaml
+package-lock.json
+dist/
+.DS_Store
+

.npmignore

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+.git
+.gitignore
+.DS_Store
+node_modules/
+bun.lockb
+pnpm-lock.yaml
+package-lock.json
+opencode.json
+test-*.mjs
+*.log
+.vscode/
+.idea/
+docs/
+.github/

LICENSE

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+MIT License
+
+Copyright (c) 2025 Numman Ali
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# 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
+
+### From npm (Recommended)
+
+```bash
+npm install opencode-openai-codex-auth
+```
+
+Add the plugin to your `opencode.json`:
+
+```json
+{
+  "$schema": "https://opencode.ai/config.json",
+  "plugin": [
+    "opencode-openai-codex-auth"
+  ],
+  "model": "openai/gpt-5-codex"
+}
+```
+
+### From source
+
+1. Clone this repository:
+
+```bash
+git clone https://github.com/numman/opencode-openai-codex-auth.git
+cd opencode-openai-codex-auth
+npm install
+```
+
+2. Add the plugin to your `opencode.json`:
+
+```json
+{
+  "$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:
+
+```bash
+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
+
+```bash
+# 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](https://github.com/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:
+- [ben-vargas/ai-sdk-provider-chatgpt-oauth](https://github.com/ben-vargas/ai-sdk-provider-chatgpt-oauth)
+- [ben-vargas/ai-opencode-chatgpt-auth](https://github.com/ben-vargas/ai-opencode-chatgpt-auth)
+- [openai/codex](https://github.com/openai/codex) OAuth flow
+- [sst/opencode](https://github.com/sst/opencode)
+
+## License
+
+MIT