platform/plugins/offscale/sidecar/enroll.ts

import type { OfficerContext } from './routes';
import type { OfficerUser } from './normalize';
import { getActiveHeadscaleCredentials } from '../db/queries';
import { badRequest, methodNotAllowed, readJson } from './routes';
import { createClient, type HeadscaleClient } from './client';
import { arrayField, toUser } from './normalize';
import { handleInvitesRoute } from './invites';

// Device enrolment — POST /_officer/enroll. The mobile app's one-tap join: it turns an authenticated
// Officer session into a short-lived, single-use pre-auth key, so nobody pastes a key by hand.
//
// THIS USED TO LIVE IN THE PLATFORM. `src/servers/api/vpn/router.ts` (deleted 2026-08-14) read
// HEADSCALE_URL, HEADSCALE_API_KEY
// and HEADSCALE_USER straight from the host env — three globals that could only ever describe ONE server,
// while this sidecar already kept a registry of many. Worse, the two credential vars were removed at some
// point and nobody noticed: the route had been answering 503 to every enrolment attempt, because it checks
// those two before it gets anywhere near the user name. Enrolment acts on the ACTIVE registered server now,
// like every other domain route here, and the platform holds no Headscale credentials at all.
//
// The response shape `{controlUrl, authKey}` is a CONTRACT: enrollVpn() in the mobile core
// (monorepo-mobile/packages/core/src/services/officer-net.ts) destructures exactly those two fields and
// feeds them to configure()/loginWithAuthKey(). Extra fields are safe; renaming those two is not.

/** Short by design: the key is redeemed seconds after it is issued, and a leaked one should die quickly. */
const KEY_TTL_MS = 10 * 60_000;

/**
 * Which Headscale user the joining device is filed under.
 *
 * An explicit `userId` wins. Otherwise the choice is only made when it is UNAMBIGUOUS — one user on the
 * server means there is nothing to choose. Several means the caller has to say, because picking silently
 * files someone's phone under the wrong owner and the mistake stays invisible until somebody audits the
 * tailnet. The old env var picked one name for every server at once, which is precisely that bug.
 */
async function resolveOwner(client: HeadscaleClient, ctx: OfficerContext): Promise<OfficerUser | Response> {
  const body = await readJson(ctx.req);
  const requested = typeof body?.userId === 'string' ? body.userId.trim() : '';

  const listed = await client.call('/api/v1/user');
  const users = arrayField(listed, 'users')
    .map(toUser)
    .filter((u): u is OfficerUser => !!u);

  if (requested) {
    const match = users.find((u) => u.id === requested);
    return match ?? badRequest(`no Headscale user with id ${requested} on the active server`);
  }

  if (users.length === 1) return users[0]!;

  if (users.length === 0) {
    return Response.json(
      { error: 'the active Headscale server has no users — create one before enrolling a device', code: 'no_users' },
      { status: 409 },
    );
  }

  return Response.json(
    {
      error: 'the active Headscale server has several users — pass userId to say which one owns this device',
      code: 'ambiguous_user',
      users: users.map((u) => ({ id: u.id, name: u.name })),
    },
    { status: 409 },
  );
}

export async function handleEnrollRoute(ctx: OfficerContext, segments: string[]): Promise<Response | null> {
  // `/enroll/invites…` is the admin invite surface — a different flow entirely (see invites.ts): the device
  // is not here and there is no Officer session on it. Same prefix because it is the same feature to the
  // person using it, and because the spec names it that way.
  if (segments[0] === 'invites') return handleInvitesRoute(ctx, segments.slice(1));

  if (segments.length > 0) return null;
  if (ctx.req.method !== 'POST') return methodNotAllowed();

  // Not activeClient(): the control URL goes back to the device, and only the credentials carry it.
  const creds = await getActiveHeadscaleCredentials(ctx.userId);
  if (!creds) {
    return Response.json({ error: 'no active Headscale server', code: 'no_active_server' }, { status: 409 });
  }

  const client = createClient(creds);

  const owner = await resolveOwner(client, ctx);
  if (owner instanceof Response) return owner;

  const created = await client.call<{ preAuthKey?: { key?: string } }>('/api/v1/preauthkey', {
    method: 'POST',
    body: {
      user: owner.id,
      reusable: false, // one key, one device
      ephemeral: false, // the node stays registered after it disconnects
      expiration: new Date(Date.now() + KEY_TTL_MS).toISOString(), // RFC3339
    },
  });

  const authKey = created.preAuthKey?.key;
  if (!authKey) return Response.json({ error: 'headscale returned no key' }, { status: 502 });

  // `server` and `user` are advisory — for a UI that wants to say what the device just joined.
  return Response.json({ controlUrl: creds.url, authKey, server: creds.name, user: owner.name });
}