feat(admin): let a token read the growth scoreboard without a session

The weekly digest reads /api/admin/growth from a script, which has no browser
and therefore no NextAuth session. The alternative was copying a session cookie
out of a browser by hand: those are JWTs with a 30-day lifetime, so a scheduled
job built on one stops working a month later and reports nothing rather than
reporting a failure.

The token path is off unless OPENFRAME_ADMIN_API_TOKEN is set, so an instance
that never sets it keeps session-only admin access. A value under 32 characters
is treated as no token at all: behind this header sit every paying account's
name, email and usage, and a short token is a guessable path to all of it.
Comparison runs over SHA-256 digests so it stays constant time without leaking
the token's length.

tests/unit/lib/admin-api-token.test.ts

@@ -0,0 +1,80 @@
+// The guard that lets a script read admin data without a session.
+//
+// Every case here is a way the endpoint could end up open: a token short enough
+// to guess, a comparison that accepts a prefix, or an absent env var read as an
+// absent header and waved through.
+
+import { describe, expect, it, afterEach, vi } from 'vitest';
+import {
+  MIN_ADMIN_API_TOKEN_LENGTH,
+  getAdminApiToken,
+  isAdminApiTokenRequest,
+} from '@/lib/admin-api-token';
+
+// Written out rather than generated from the constant: a test whose input comes
+// from the code under test stops testing the length rule the moment it changes.
+const TOKEN = 'zq4Xr7Tn2Vb9Kd5Mw8Hs3Lp6Cf1Gj0Ye';
+const SHORT = 'zq4Xr7Tn2Vb9Kd5Mw8Hs3Lp6Cf1Gj0Y';
+
+function requestWith(headers: Record<string, string>): Request {
+  return new Request('http://localhost:3000/api/admin/growth', { headers });
+}
+
+afterEach(() => {
+  vi.unstubAllEnvs();
+});
+
+describe('getAdminApiToken', () => {
+  it('is null when nothing is configured', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', '');
+    expect(getAdminApiToken()).toBeNull();
+  });
+
+  it('is null for a token shorter than the minimum', () => {
+    expect(SHORT).toHaveLength(MIN_ADMIN_API_TOKEN_LENGTH - 1);
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', SHORT);
+    expect(getAdminApiToken()).toBeNull();
+  });
+
+  it('trims surrounding whitespace, which a pasted env value carries', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', `  ${TOKEN}\n`);
+    expect(getAdminApiToken()).toBe(TOKEN);
+  });
+});
+
+describe('isAdminApiTokenRequest', () => {
+  it('refuses every request when no token is configured', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', '');
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `Bearer ${TOKEN}` }))).toBe(false);
+    expect(isAdminApiTokenRequest(requestWith({}))).toBe(false);
+  });
+
+  it('refuses a matching header when the configured token is too short', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', SHORT);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `Bearer ${SHORT}` }))).toBe(false);
+  });
+
+  it('accepts the configured token, whatever case the scheme is written in', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', TOKEN);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `Bearer ${TOKEN}` }))).toBe(true);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `bearer ${TOKEN}` }))).toBe(true);
+  });
+
+  it('refuses a prefix, a suffix and a different token of the same length', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', TOKEN);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `Bearer ${SHORT}` }))).toBe(false);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `Bearer ${TOKEN}x` }))).toBe(false);
+    expect(
+      isAdminApiTokenRequest(
+        requestWith({ authorization: 'Bearer aq4Xr7Tn2Vb9Kd5Mw8Hs3Lp6Cf1Gj0Ye' })
+      )
+    ).toBe(false);
+  });
+
+  it('refuses a missing header, a bare token and another scheme', () => {
+    vi.stubEnv('OPENFRAME_ADMIN_API_TOKEN', TOKEN);
+    expect(isAdminApiTokenRequest(requestWith({}))).toBe(false);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: TOKEN }))).toBe(false);
+    expect(isAdminApiTokenRequest(requestWith({ authorization: `Basic ${TOKEN}` }))).toBe(false);
+  });
+});