opencode-antigravity-auth-setup

name	opencode-antigravity-auth-setup
description	Configure OpenCode + opencode-antigravity-auth plugin to use Google OAuth (Antigravity) for free Gemini/Claude usage; includes auth-store gotchas, verified workaround, and troubleshooting with logs.

Opencode Antigravity Auth Setup

[Created by Codex: 019ba92d-c995-77c0-b090-e9109492f53b]

Overview

Enable OpenCode to call Antigravity-backed models (Gemini 3 + Claude) using Google OAuth tokens, without API keys, via the opencode-antigravity-auth plugin.

Key Findings (What Broke)

• OpenCode stores provider credentials in ~/.local/share/opencode/auth.json.
• OpenCode only runs the plugin’s auth.loader for google if a google credential already exists in that auth store.
• If there is no google credential, OpenCode uses bundled @ai-sdk/google, which requires GOOGLE_GENERATIVE_AI_API_KEY and fails with AI_LoadAPIKeyError.
• opencode auth login google is not a provider shortcut. opencode auth login [url] treats the arg as a URL and tries /.well-known/opencode (so google causes ERR_INVALID_URL).

Workflow (Verified)

1) Install/enable plugin + models

• Ensure ~/.config/opencode/opencode.json contains:
  • "plugin": ["opencode-antigravity-auth@beta"]
  • provider "google" models using the antigravity- prefix (recommended).
• Confirm models are visible:
  • opencode models google

2) Create a google OAuth credential (required for plugin loader)

• Run opencode auth login (no args).
• Select provider: Google.
• Select method: OAuth with Google (Antigravity).
• Verify:
  • opencode auth list shows Google oauth.

3) Bootstrap workaround (verified)

If ~/.config/opencode/antigravity-accounts.json already exists (refresh tokens saved) but opencode auth list shows no credentials, bootstrap the google OAuth entry:

python ~/.codex/skills/opencode-antigravity-auth-setup/scripts/bootstrap_opencode_google_oauth.py

This writes a minimal stub to ~/.local/share/opencode/auth.json:

• google.type=oauth
• google.refresh="<refreshToken>|<projectId>|<managedProjectId>"
• google.access="", google.expires=0 (the plugin refreshes on first use)

4) Run a model

opencode run "hello" --model=google/antigravity-gemini-3-pro

Troubleshooting

Symptom: AI_LoadAPIKeyError / “Google Generative AI API key is missing”

• Cause: plugin loader not running (no google credential in ~/.local/share/opencode/auth.json)
• Fix: run Workflow step (2) or (3)

Symptom: OpenCode shows “Waiting for authorization…” forever

• Use the manual fallback flow (CLI prompt), or use the bootstrap script above.
• Check whether OpenCode actually stored the credential:
  • opencode auth list

Symptom: opencode auth login google fails

• Expected. Use opencode auth login without args.

Reference (Investigation)

• Read the investigation handoff at references/investigation-opencode-antigravity-auth.md.