OpenCode Gemini CLI OAuth Plugin

Use Gemini models in OpenCode with your Google account quota - no API keys needed!

This plugin integrates Gemini CLI's OAuth authentication with OpenCode, allowing you to use Google's free Gemini quota without generating API keys.

✨ Features

• 🔐 OAuth Authentication - Reuses Gemini CLI credentials from ~/.gemini/oauth_creds.json
• 👥 Multi-Account Support - Automatic rotation across multiple Google accounts
• 🔄 Auto Token Refresh - Handles expired tokens seamlessly
• 🚦 Rate Limit Handling - Auto-switches to next account when rate limited
• 🤝 Antigravity Compatible - Works alongside opencode-antigravity-auth plugin
• 🆓 Free Quota - Use Google's free tier quota (1,500 requests/day per account)

📦 Installation

Prerequisites

1. Gemini CLI must be installed and authenticated:

   npm install -g @google/gemini-cli
   gemini auth login  # Authenticate with your Google account

2. OpenCode v1.0.0 or higher

Install Plugin

# Install globally from NPM
npm install -g opencode-gemini-cli-oauth

⚡ Easy Setup (Recommended)

Run the setup wizard to automatically configure OpenCode with Gemini models:

opencode-gemini-setup

This will:

1. Check your Gemini CLI authentication
2. Login if needed
3. Configure opencode.json with the latest models (Gemini 2.0, 1.5, etc.)

Manual Configuration

If you prefer to configure manually, add to ~/.config/opencode/opencode.json:

{
  "plugin": [
    "opencode-antigravity-auth@beta",
    "opencode-gemini-cli-oauth"
  ],
  "provider": {
    "gemini-cli-oauth": {
      "npm": "@ai-sdk/google",
      "models": {
        "gemini-2.5-flash-exp": {
          "name": "Gemini 2.5 Flash (Google Account)",
          "limit": { "context": 1048576, "output": 65536 },
          "modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }
        }
      }
    }
  }
}

🚀 Usage

1. Authenticate with Gemini CLI

# Login with your Google account
gemini auth login

# Verify authentication
gemini "hello"

2. Launch OpenCode

opencode

3. Select Model

In OpenCode:

• Press Ctrl+P → "Switch Model"
• Choose "Gemini 2.5 Flash (Google Account)" or any model with "(Google Account)"
• Start chatting!

🔀 3-Way Authentication Options

After installing this plugin, you have 3 authentication methods for Google models:

| Method | Provider | Models | Source | Quota | |--------|----------|--------|--------|-------| | 1. Google Account (OAuth) | gemini-cli-oauth | Gemini 2.5 Flash/Pro, Gemini 2.0 Flash | This plugin | Google account free tier | | 2. API Key | google-api-key | Gemini 1.5/2.5 models | Generated from AI Studio | API key quota | | 3. Antigravity | google | Gemini 3 Pro/Flash, Claude Sonnet/Opus | opencode-antigravity-auth | Antigravity quota |

All three can coexist without conflicts!

👥 Multi-Account Setup

To rotate across multiple Google accounts:

1. Authenticate each account with Gemini CLI:

   gemini auth login  # Login with account 1
   # Complete OAuth flow
   
   # Repeat for more accounts (Gemini CLI will store them)

2. Plugin automatically rotates between accounts when:

   • An account hits rate limit (429 error)
   • Distributing requests evenly

3. Check account pool:

   cat ~/.gemini/opencode-plugin/account_pool.json

🔧 How It Works

1. OAuth Token Injection

   • Plugin reads credentials from ~/.gemini/oauth_creds.json (created by Gemini CLI)
   • Injects Authorization: Bearer <access_token> header to Gemini API requests
   • Removes ?key= parameter from URLs (OAuth doesn't need it)

2. Request Interception

   • Only intercepts requests to generativelanguage.googleapis.com
   • Other providers (Antigravity, standard Google) are unaffected

3. Token Refresh

   • Monitors token expiry (expiry_date field)
   • Auto-refreshes 5 minutes before expiration
   • Uses refresh_token to get new access_token

4. Rate Limit Handling

   • Detects 429 responses
   • Marks account as rate-limited with retry-after timestamp
   • Switches to next available account
   • Retries request automatically

📊 Quota Management

Free Tier Limits (per Google account):

• Requests: 1,500 requests/day
• Tokens: 1,000,000 tokens/day
• RPM: 15 requests/minute (Gemini 2.5 Flash)

With 5 accounts, you get:

• 7,500 requests/day
• 5,000,000 tokens/day
• Automatic rotation on rate limits

🐛 Troubleshooting

"No OAuth credentials found"

# Re-authenticate with Gemini CLI
gemini auth login

"Failed to refresh access token"

# Clear cached credentials and re-auth
rm ~/.gemini/oauth_creds.json
gemini auth login

Plugin not loading

# Check plugin is installed
npm list -g opencode-gemini-cli-oauth

# Re-link if needed
cd ~/projects/opencode-gemini-cli-oauth
npm link

Rate limited on all accounts

# Check account pool status
cat ~/.gemini/opencode-plugin/account_pool.json

# Clear rate limit timestamps
echo '{"accounts":[],"currentIndex":0}' > ~/.gemini/opencode-plugin/account_pool.json

# Or wait for retry-after period to expire

🔒 Security Notes

1. OAuth credentials are stored locally in ~/.gemini/oauth_creds.json
2. Client ID/Secret are public (safe for "installed applications" per Google OAuth guidelines)
3. Tokens auto-refresh - no manual intervention needed
4. No credentials sent to third parties - direct Google API communication only

📚 API Reference

Exported Classes

import {
  OAuthManager,        // OAuth token management
  AccountManager,      // Multi-account rotation
  StorageManager,      // Credentials storage
} from 'opencode-gemini-cli-oauth';

// Example: Get current access token
const oauthManager = new OAuthManager();
const token = await oauthManager.getAccessToken();

// Example: Check account pool stats
const accountManager = new AccountManager();
const stats = await accountManager.getPoolStats();
console.log(stats); // { totalAccounts: 5, availableAccounts: 4, rateLimitedAccounts: 1 }

🤝 Contributing

Contributions welcome! Please:

1. Fork the repository
2. Create a feature branch
3. Submit a pull request

📄 License

MIT License - see LICENSE file for details

🙏 Credits

• Built by @yusuf
• Inspired by opencode-antigravity-auth
• Uses Google Auth Library

🔗 Related Projects

• Gemini CLI - Official Google Gemini CLI
• OpenCode - AI-powered code editor
• OpenCode Antigravity Auth - Antigravity integration

Made with ❤️ for the OpenCode community