Opencode Claude Auth

---
name: opencode-claude-auth
description: OpenCode plugin that reuses Claude Code OAuth credentials for Anthropic API access — no separate API key needed
triggers:
  - use Claude Code credentials with OpenCode
  - authenticate OpenCode with Claude subscription
  - opencode-claude-auth plugin setup
  - reuse Claude Pro credentials in OpenCode
  - OpenCode no API key auth
  - set up opencode claude auth plugin
  - Claude Code OAuth token for OpenCode
  - opencode anthropic auth without API key
---

# opencode-claude-auth

> Skill by [ara.so](https://ara.so) — Daily 2026 Skills collection.

A self-contained Anthropic auth provider for OpenCode that reads your existing Claude Code OAuth credentials — no separate API key or login needed. Works on macOS (Keychain), Linux, and Windows (`~/.claude/.credentials.json`).

## How It Works

1. Registers a custom `auth.loader` with OpenCode that intercepts all Anthropic API calls
2. Reads OAuth tokens from macOS Keychain or `~/.claude/.credentials.json`
3. Caches tokens in memory (30s TTL), refreshes via `claude` CLI when near expiry
4. Syncs credentials to OpenCode's `auth.json` as fallback every 5 minutes
5. Handles tool name translation, SSE stream buffering, retry logic (429/529), and required headers

## Prerequisites

- Claude Code installed and authenticated (`claude` run at least once)
- OpenCode installed

## Installation

### Global npm install

```bash
npm install -g opencode-claude-auth

Register the plugin in opencode.json

{
  "plugin": ["opencode-claude-auth"]
}

That's it — run OpenCode normally. Auth is automatic.

AI-assisted install (paste into any agent)

Fetch https://raw.githubusercontent.com/griffinmartin/opencode-claude-auth/main/installation.md and follow every step exactly as written.

Configuration

No configuration required by default. All parameters have sensible defaults and can be overridden via environment variables:

# Override CLI version if Anthropic updates their API before a new plugin release
export ANTHROPIC_CLI_VERSION=2.2.0

# Override full user agent
export ANTHROPIC_USER_AGENT="claude-cli/2.2.0 (external, cli)"

# Override beta flags
export ANTHROPIC_BETA_FLAGS="claude-code-20250219,oauth-2025-04-20"

Supported Models

claude-3-haiku-20240307
claude-haiku-4-5
claude-haiku-4-5-20251001
claude-opus-4-0
claude-opus-4-1
claude-opus-4-1-20250805
claude-opus-4-20250514
claude-opus-4-5
claude-opus-4-5-20251101
claude-opus-4-6
claude-sonnet-4-0
claude-sonnet-4-20250514
claude-sonnet-4-5
claude-sonnet-4-5-20250929
claude-sonnet-4-6

Verify models against your account:

npm run test:models

Credential Sources (checked in order)

1. macOS Keychain — entry named "Claude Code-credentials" (preferred)
2. ~/.claude/.credentials.json — fallback, works on all platforms

If credentials aren't OAuth-based, the plugin falls through to standard API key auth. If credentials are unavailable, the plugin disables itself gracefully.

opencode.json Full Example

{
  "model": "claude-sonnet-4-5",
  "plugin": ["opencode-claude-auth"],
  "experimental": {
    "chat": {
      "system": {
        "transform": true
      }
    }
  }
}

What the Plugin Does Internally

// The plugin registers an auth loader that intercepts Anthropic requests:
// - Reads OAuth token from Keychain or credentials file
// - Caches in memory with 30s TTL
// - Sets Authorization: Bearer <token>
// - Injects required headers:
//   x-api-key, anthropic-version, anthropic-beta, user-agent, x-stainless-*
// - Translates tool names: OpenCode uses mcp_ prefix, API does not
// - Buffers SSE streams at event boundaries for safe translation
// - Retries on 429/529 with exponential backoff + retry-after header
// - Runs `claude` CLI to refresh tokens expiring within 60s
// - Syncs to auth.json every 5 minutes as fallback
// - On Windows: writes to both %USERPROFILE%\.local\share\opencode\auth.json
//   and %LOCALAPPDATA%\opencode\auth.json

Troubleshooting

Verify credentials file exists (Linux/Windows)

cat ~/.claude/.credentials.json

Unlock macOS Keychain manually

security unlock-keychain ~/Library/Keychains/login.keychain-db

Force credential refresh

claude  # triggers OAuth refresh, plugin picks up new token within 30s

Common Patterns

Minimal setup for a new machine

# 1. Authenticate Claude Code
claude

# 2. Install OpenCode (if not done)
# See OpenCode docs for platform-specific install

# 3. Install plugin
npm install -g opencode-claude-auth

# 4. Add to opencode.json
cat > opencode.json << 'EOF'
{
  "plugin": ["opencode-claude-auth"]
}
EOF

# 5. Run OpenCode — auth is automatic
opencode

Using a specific model

{
  "model": "claude-opus-4-5",
  "plugin": ["opencode-claude-auth"]
}

Handling API version changes without waiting for a plugin update

# If Anthropic bumps their CLI version requirement:
export ANTHROPIC_CLI_VERSION=2.3.0
# Plugin will use this in user-agent and billing headers immediately

CI / non-interactive environments

The plugin requires ~/.claude/.credentials.json to exist (created by running claude interactively). For CI, copy the credentials file from a pre-authenticated environment or use a standard ANTHROPIC_API_KEY instead (the plugin falls through to API key auth when no OAuth credentials are present).

Disclaimer

This plugin uses Claude Code's OAuth credentials. Anthropic's Terms of Service restrict Claude Pro/Max subscription tokens to official clients. This is a community workaround that may break if Anthropic changes their OAuth infrastructure. Use at your own discretion.