opencode-claude-auth

Self-contained Anthropic auth provider for OpenCode using your Claude Code credentials — no separate login or API key needed.

How it works

The plugin registers its own auth provider with a custom fetch handler that intercepts all Anthropic API requests. It reads OAuth tokens from the macOS Keychain (or ~/.claude/.credentials.json on other platforms), caches them in memory with a 30-second TTL, and handles the full request lifecycle — no builtin Anthropic auth plugin required.

It also syncs credentials to OpenCode's auth.json as a fallback (on Windows, it writes to both %USERPROFILE%\.local\share\opencode\auth.json and %LOCALAPPDATA%\opencode\auth.json to cover all installation methods). If a token is near expiry, it runs the Claude CLI to trigger a refresh. Background re-sync runs every 5 minutes.

Prerequisites

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

macOS is preferred (uses Keychain). Linux and Windows work via the credentials file fallback.

Installation

Install with AI

Paste this into your AI agent (Claude Code, Cursor, Copilot, etc.):

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

Manual install

npm install -g opencode-claude-auth

Then add to the plugin array in your opencode.json:

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

Usage

Just run OpenCode. The plugin handles auth automatically — it reads your Claude Code credentials, provides them to the Anthropic API, and refreshes them in the background. If your credentials aren't OAuth-based, the plugin falls through to standard API key auth.

Supported models

15 supported models. Run npm run test:models to verify against your account.

Model
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

Credential sources

The plugin checks these in order:

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

Troubleshooting

Problem	Solution
"Credentials not found"	Run claude to authenticate with Claude Code first
"Keychain is locked"	Run security unlock-keychain ~/Library/Keychains/login.keychain-db
"Token expired and refresh failed"	The plugin runs claude CLI to refresh automatically. If this fails, re-authenticate manually by running claude
Not working on Linux/Windows	Ensure ~/.claude/.credentials.json exists. Run claude to create it
Keychain access denied	Grant access when macOS prompts you
Keychain read timed out	Restart Keychain Access (can happen on macOS Tahoe)
"Credentials are unavailable or expired"	Run claude to refresh your Claude Code credentials

Environment variable overrides

All configurable parameters can be overridden via environment variables. If Anthropic changes something before we publish an update, set an env var and keep working:

Variable	Description	Default
ANTHROPIC_CLI_VERSION	Claude CLI version for user-agent and billing headers	2.1.80
ANTHROPIC_USER_AGENT	Full User-Agent string (overrides CLI version)	claude-cli/{version} (external, cli)
ANTHROPIC_BETA_FLAGS	Comma-separated beta feature flags	claude-code-20250219,oauth-2025-04-20,interleaved-thinking-2025-05-14,prompt-caching-scope-2026-01-05

Example:

export ANTHROPIC_CLI_VERSION=2.2.0

How it works (technical)

• Registers an auth.loader with a custom fetch that intercepts all Anthropic API requests
• Sets Authorization: Bearer with fresh OAuth tokens (cached in memory, 30s TTL)
• Translates tool names between OpenCode and Anthropic API formats (adds/strips mcp_ prefix)
• Buffers SSE response streams at event boundaries for reliable tool name translation
• Injects Claude Code identity into system prompts via experimental.chat.system.transform
• Sets required API headers (beta flags, billing, user-agent) with model-aware selection
• Syncs credentials to auth.json on startup and every 5 minutes as a fallback
• On Windows, writes to both %USERPROFILE%\.local\share\opencode\auth.json and %LOCALAPPDATA%\opencode\auth.json
• Retries API requests on 429 (rate limit) and 529 (overloaded) with exponential backoff, respecting retry-after headers
• When a token is within 60 seconds of expiry, runs claude CLI to trigger a refresh (with one automatic retry)
• If credentials aren't OAuth-based, the auth loader returns {} and falls through to API key auth
• If credentials are unavailable or unreadable, the plugin disables itself and OpenCode continues without Claude auth

Disclaimer

This plugin uses Claude Code's OAuth credentials to authenticate with Anthropic's API. Anthropic's Terms of Service state that Claude Pro/Max subscription tokens should only be used with official Anthropic clients. This plugin exists as a community workaround and may stop working if Anthropic changes their OAuth infrastructure. Use at your own discretion.

License

MIT