opencode-cursor-auth

OpenCode plugin that connects to Cursor's API, giving you access to all Cursor models (Composer 2, Claude, GPT, Gemini, etc.) inside OpenCode with full tool calling support.

How it works

1. OAuth -- Browser-based login to your Cursor account via PKCE flow.
2. Model discovery -- Queries Cursor's gRPC API for all available models.
3. Local proxy -- Starts a localhost OpenAI-compatible server that translates POST /v1/chat/completions into Cursor's protobuf/HTTP2 Connect protocol.
4. Native tool routing -- Cursor models try their built-in tools first (read, shell, grep, etc.). The proxy rejects those and exposes OpenCode's tools via Cursor's MCP protocol instead.

HTTP/2 transport runs through a Node child process (h2-bridge.mjs) because Bun's node:http2 module is broken.

Setup

1. Install dependencies

cd opencode-cursor
bun install

2. Register the plugin

Add to ~/.config/opencode/opencode.json:

{
  "plugin": [
    // ... other plugins
    "file:///path/to/opencode-cursor/src/index.ts"
  ],
  "provider": {
    // ... other providers
    "cursor": {
      "name": "Cursor"
    }
  }
}

The cursor provider stub is required -- OpenCode's mergeProvider() silently drops providers not in the models.dev database unless a config entry exists.

3. Authenticate

opencode auth login --provider cursor

Opens a browser window for Cursor OAuth. Tokens are stored in ~/.local/share/opencode/auth.json and refreshed automatically.

4. Use

Start OpenCode and select any Cursor model. The proxy starts on a random port when the plugin loads.

Architecture

OpenCode  -->  /v1/chat/completions  -->  Bun.serve (proxy)
                                              |
                                    Node child process (h2-bridge.mjs)
                                              |
                                     HTTP/2 Connect stream
                                              |
                                    api2.cursor.sh gRPC
                                      /agent.v1.AgentService/Run

Tool call flow

1. Cursor model receives OpenAI tools via RequestContext (as MCP tool defs)
2. Model tries native tools (readArgs, shellArgs, etc.)
3. Proxy rejects each with typed error (ReadRejected, ShellRejected, etc.)
4. Model falls back to MCP tool → mcpArgs exec message
5. Proxy emits OpenAI tool_calls SSE chunk, pauses H2 stream
6. OpenCode executes tool, sends result in follow-up request
7. Proxy resumes H2 stream with mcpResult, streams continuation

Files

File	Purpose
src/index.ts	Plugin entry -- auth hook, model injection, proxy lifecycle
src/proxy.ts	OpenAI-to-Cursor translator, native tool rejection, MCP bridging
src/h2-bridge.mjs	Node child process for HTTP/2 bidirectional streaming
src/auth.ts	Cursor OAuth (PKCE, polling, token refresh)
src/models.ts	Model discovery via gRPC GetUsableModels
src/pkce.ts	PKCE verifier/challenge generation
src/proto/agent_pb.ts	Cursor protobuf definitions (generated)
test/smoke.ts	Proxy, auth, and plugin shape tests

Tests

bun test/smoke.ts

Requirements

• Bun (runtime)
• Node.js >= 18 (for HTTP/2 bridge)
• Active Cursor subscription