singularity-forge/web/lib/auth.ts

/**
 * Client-side auth token management.
 *
 * The web server generates a random bearer token at launch and passes it to
 * the browser via the URL fragment (e.g. `http://127.0.0.1:3000/#token=<hex>`).
 * Fragments are never sent in HTTP requests or logged by servers/proxies,
 * keeping the token local to the machine.
 *
 * On first load this module extracts the token from the fragment, persists
 * it to localStorage (so it survives page refreshes and is accessible from
 * all tabs on the same origin), and clears the fragment from the address bar.
 * All subsequent API calls attach the token via the `Authorization: Bearer`
 * header.
 *
 * localStorage is shared across all tabs on the same origin. Because each
 * SF instance binds to a unique random port, the origin already scopes
 * the token to that instance — no additional namespacing is needed.
 *
 * For EventSource (SSE), which cannot send custom headers, the token is
 * appended as a `?_token=` query parameter instead.
 */

const AUTH_STORAGE_KEY = "sf-auth-token";

let cachedToken: string | null = null;

/**
 * Extract the auth token from the URL fragment, localStorage, or prompt for login.
 * If not found, redirect to /login page.
 */
export function getAuthToken(): string | null {
	if (cachedToken !== null) return cachedToken;

	if (typeof window === "undefined") return null;

	// 1. Try the URL fragment (initial page load from sf --web)
	const hash = window.location.hash;
	if (hash) {
		const match = hash.match(/token=([a-fA-F0-9]+)/);
		if (match) {
			cachedToken = match[1];
			try {
				localStorage.setItem(AUTH_STORAGE_KEY, cachedToken);
			} catch {}
			window.history.replaceState(
				null,
				"",
				window.location.pathname + window.location.search,
			);
			return cachedToken;
		}
	}

	// 2. Fall back to localStorage
	try {
		const stored = localStorage.getItem(AUTH_STORAGE_KEY);
		if (stored) {
			cachedToken = stored;
			return cachedToken;
		}
	} catch {}

	// 3. If not found, redirect to login
	if (window.location.pathname !== "/login") {
		window.location.href = "/login";
	}
	return null;
}

/**
 * Listen for token changes from other tabs via the `storage` event.
 * When another tab writes a new token to localStorage, this tab picks
 * it up immediately without requiring a page refresh.
 */
if (typeof window !== "undefined") {
	window.addEventListener("storage", (event) => {
		if (event.key === AUTH_STORAGE_KEY && event.newValue) {
			cachedToken = event.newValue;
		}
	});
}

/**
 * Returns an object with the `Authorization` header for use with `fetch()`.
 * Merges with any additional headers provided.
 */
export function authHeaders(
	extra?: Record<string, string>,
): Record<string, string> {
	const token = getAuthToken();
	const headers: Record<string, string> = { ...extra };
	if (token) {
		headers["Authorization"] = `Bearer ${token}`;
	}
	return headers;
}

/**
 * Wrapper around `fetch()` that automatically injects the auth token.
 *
 * When no token is available (missing `#token=` fragment and no localStorage
 * entry), returns a synthetic 401 Response instead of making an unauthenticated
 * request that will fail server-side anyway. This lets callers handle the
 * missing-token case uniformly rather than silently cascading 401s.
 */
export async function authFetch(
	input: RequestInfo | URL,
	init?: RequestInit,
): Promise<Response> {
	const token = getAuthToken();
	if (!token) {
		return new Response(JSON.stringify({ error: "No auth token available" }), {
			status: 401,
			headers: { "Content-Type": "application/json" },
		});
	}

	const headers = new Headers(init?.headers);
	if (!headers.has("Authorization")) {
		headers.set("Authorization", `Bearer ${token}`);
	}

	return fetch(input, { ...init, headers });
}

/**
 * Append the auth token as a `_token` query parameter to a URL string.
 * Used for EventSource connections which cannot send custom headers.
 */
export function appendAuthParam(url: string): string {
	const token = getAuthToken();
	if (!token) return url;

	const separator = url.includes("?") ? "&" : "?";
	return `${url}${separator}_token=${token}`;
}