Heartwood Auth Integration Skill

When to Activate

Activate this skill when:

• Adding authentication to a Grove application
• Protecting admin routes
• Validating user sessions
• Setting up OAuth sign-in
• Integrating with Heartwood (GroveAuth)

Overview

Heartwood is Grove's centralized authentication service powered by Better Auth.

Domain	Purpose
heartwood.grove.place	Frontend (login UI)
auth-api.grove.place	Backend API

Key Features

• OAuth Providers: Google
• Magic Links: Click-to-login emails via Resend
• Passkeys: WebAuthn passwordless authentication
• KV-Cached Sessions: Sub-100ms validation
• Cross-Subdomain SSO: Single session across all .grove.place

Integration Approaches

Option A: Better Auth Client (Recommended)

For new integrations, use Better Auth's client library:

// src/lib/auth/client.ts
import { createAuthClient } from "better-auth/client";

export const auth = createAuthClient({
	baseURL: "https://auth-api.grove.place",
});

// Sign in with Google
await auth.signIn.social({ provider: "google" });

// Get current session
const session = await auth.getSession();

// Sign out
await auth.signOut();

Option B: Cookie-Based SSO (*.grove.place apps)

For apps on .grove.place subdomains, sessions work automatically via cookies:

// src/hooks.server.ts
import type { Handle } from "@sveltejs/kit";

export const handle: Handle = async ({ event, resolve }) => {
	// Check session via Heartwood API
	const sessionCookie = event.cookies.get("better-auth.session_token");

	if (sessionCookie) {
		try {
			const response = await fetch("https://auth-api.grove.place/api/auth/session", {
				headers: {
					Cookie: `better-auth.session_token=${sessionCookie}`,
				},
			});

			if (response.ok) {
				const data = await response.json();
				event.locals.user = data.user;
				event.locals.session = data.session;
			}
		} catch {
			// Session invalid, expired, or network error — silently continue
		}
	}

	return resolve(event);
};

Option C: Legacy Token Flow (Backwards Compatible)

For existing integrations using the legacy OAuth flow:

// 1. Redirect to Heartwood login
const params = new URLSearchParams({
	client_id: "your-client-id",
	redirect_uri: "https://yourapp.grove.place/auth/callback",
	state: crypto.randomUUID(),
	code_challenge: await generateCodeChallenge(verifier),
	code_challenge_method: "S256",
});
redirect(302, `https://auth-api.grove.place/login?${params}`);

// 2. Exchange code for tokens (in callback route)
const tokens = await fetch("https://auth-api.grove.place/token", {
	method: "POST",
	headers: { "Content-Type": "application/x-www-form-urlencoded" },
	body: new URLSearchParams({
		grant_type: "authorization_code",
		code: code,
		redirect_uri: "https://yourapp.grove.place/auth/callback",
		client_id: "your-client-id",
		client_secret: env.HEARTWOOD_CLIENT_SECRET,
		code_verifier: verifier,
	}),
}).then((r) => r.json());

// 3. Verify token on protected routes
const user = await fetch("https://auth-api.grove.place/verify", {
	headers: { Authorization: `Bearer ${tokens.access_token}` },
}).then((r) => r.json());

Protected Routes Pattern

SvelteKit Layout Protection

// src/routes/admin/+layout.server.ts
import { redirect } from "@sveltejs/kit";
import type { LayoutServerLoad } from "./$types";

export const load: LayoutServerLoad = async ({ locals }) => {
	if (!locals.user) {
		throw redirect(302, "/auth/login");
	}

	return {
		user: locals.user,
	};
};

API Route Protection

// src/routes/api/protected/+server.ts
import { json, error } from "@sveltejs/kit";
import type { RequestHandler } from "./$types";

export const GET: RequestHandler = async ({ locals }) => {
	if (!locals.user) {
		throw error(401, "Unauthorized");
	}

	return json({ message: "Protected data", user: locals.user });
};

Session Validation

Via Better Auth Session Endpoint

async function validateSession(sessionToken: string) {
	const response = await fetch("https://auth-api.grove.place/api/auth/session", {
		headers: {
			Cookie: `better-auth.session_token=${sessionToken}`,
		},
	});

	if (!response.ok) return null;

	const data = await response.json();
	return data.session ? data : null;
}

Via Legacy Verify Endpoint

async function validateToken(accessToken: string) {
	const response = await fetch("https://auth-api.grove.place/verify", {
		headers: {
			Authorization: `Bearer ${accessToken}`,
		},
	});

	const data = await response.json();
	return data.active ? data : null;
}

Client Registration

To integrate a new app with Heartwood, you need to register it as a client.

1. Generate Client Credentials

# Generate a secure client secret
openssl rand -base64 32
# Example: YKzJChC3RPjZvd1f/OD5zUGAvcouOTXG7maQP1ernCg=

# Hash it for storage (base64url encoding)
echo -n "YOUR_SECRET" | openssl dgst -sha256 -binary | base64 | tr '+/' '-_' | tr -d '='

2. Register in Heartwood Database

INSERT INTO clients (id, name, client_id, client_secret_hash, redirect_uris, allowed_origins)
VALUES (
  lower(hex(randomblob(16))),
  'Your App Name',
  'your-app-id',
  'BASE64URL_HASHED_SECRET',
  '["https://yourapp.grove.place/auth/callback"]',
  '["https://yourapp.grove.place"]'
);

3. Set Secrets on Your App

# Set the client secret on your app
wrangler secret put HEARTWOOD_CLIENT_SECRET
# Paste: YKzJChC3RPjZvd1f/OD5zUGAvcouOTXG7maQP1ernCg=

Environment Variables

Variable	Description
HEARTWOOD_CLIENT_ID	Your registered client ID
HEARTWOOD_CLIENT_SECRET	Your client secret (never commit!)

API Endpoints Reference

Better Auth Endpoints (Recommended)

Method	Endpoint	Purpose
POST	/api/auth/sign-in/social	OAuth sign-in
POST	/api/auth/sign-in/magic-link	Magic link sign-in
POST	/api/auth/sign-in/passkey	Passkey sign-in
GET	/api/auth/session	Get current session
POST	/api/auth/sign-out	Sign out

Legacy Endpoints

Method	Endpoint	Purpose
GET	/login	Login page
POST	/token	Exchange code for tokens
GET	/verify	Validate access token
GET	/userinfo	Get user info

Best Practices

DO

• Use Better Auth client for new integrations
• Validate sessions on every protected request
• Use httpOnly cookies for token storage
• Implement proper error handling for auth failures
• Log out users gracefully when sessions expire

DON'T

• Store tokens in localStorage (XSS vulnerable)
• Skip session validation on API routes
• Hardcode client secrets
• Ignore token expiration

Type-Safe Error Handling

Use Rootwork type guards in catch blocks instead of manual error type narrowing. Import from @autumnsgrove/lattice/server:

import { isRedirect, isHttpError } from "@autumnsgrove/lattice/server";

try {
	// ... auth flow
} catch (err) {
	if (isRedirect(err)) throw err; // Re-throw SvelteKit redirects
	if (isHttpError(err)) {
		// Handle HTTP errors with proper status code
		console.error(`Auth failed: ${err.status} ${err.body}`);
	}
	// Fallback error handling
}

Reading session data from KV/cache: Use safeJsonParse() for type-safe deserialization:

import { safeJsonParse } from "@autumnsgrove/lattice/server";
import { z } from "zod";

const sessionSchema = z.object({
	userId: z.string(),
	email: z.string().email(),
});

const rawSession = await kv.get("session:123");
const session = safeJsonParse(rawSession, sessionSchema);

if (session) {
	event.locals.user = { id: session.userId, email: session.email };
}

Cross-Subdomain SSO

All .grove.place apps share the same session cookie automatically:

better-auth.session_token (domain=.grove.place)

Once a user signs in on any Grove property, they're signed in everywhere.

Troubleshooting

"Session not found" errors

• Check cookie domain is .grove.place
• Verify SESSION_KV namespace is accessible
• Check session hasn't expired

OAuth callback errors

• Verify redirect_uri matches registered client
• Check client_id is correct
• Ensure client_secret_hash uses base64url encoding

Slow authentication

• Ensure KV caching is enabled (SESSION_KV binding)
• Check for cold start issues (Workers may sleep)

Error Codes (HW-AUTH Catalog)

Heartwood has its own Signpost error catalog with 16 codes:

import {
	AUTH_ERRORS,
	getAuthError,
	logAuthError,
	buildErrorParams,
} from "@autumnsgrove/lattice/heartwood";

Key error codes:

Code	Key	When
HW-AUTH-001	ACCESS_DENIED	User lacks permission
HW-AUTH-002	PROVIDER_ERROR	OAuth provider failed
HW-AUTH-004	REDIRECT_URI_MISMATCH	Callback URL doesn't match registered client
HW-AUTH-020	NO_SESSION	No session cookie found
HW-AUTH-021	SESSION_EXPIRED	Session timed out
HW-AUTH-022	INVALID_TOKEN	Token verification failed
HW-AUTH-023	TOKEN_EXCHANGE_FAILED	Code-for-token exchange failed

Mapping OAuth errors to Signpost codes:

// In callback handler — map OAuth error param to structured error
const authError = getAuthError(errorParam); // e.g. "access_denied" → AUTH_ERRORS.ACCESS_DENIED
logAuthError(authError, { path: "/auth/callback", ip });
redirect(302, `/login?${buildErrorParams(authError)}`);

Number ranges: 001-019 infrastructure, 020-039 session/token, 040+ reserved.

See AgentUsage/error_handling.md for the full Signpost reference.

Related Resources

• Heartwood Spec: /Users/autumn/Documents/Projects/GroveAuth/GROVEAUTH_SPEC.md
• Better Auth Docs: https://better-auth.com
• Client Setup Guide: /Users/autumn/Documents/Projects/GroveAuth/docs/OAUTH_CLIENT_SETUP.md