GDPR right-to-be-forgotten

A complete /v1/forget flow including audit-trail patterns and what doesn't get deleted.

A user emails support: "delete all my data". This recipe walks through running that request through Millimetric end-to-end, what's actually deleted, and the audit trail you should keep on your side.

TL;DR

curl -X POST https://api.millimetric.ai/v1/forget \
  -H "Authorization: Bearer $SK_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "user_id": "user_42" }'

sk_* only. pk_* returns 403 forget_requires_secret_key — a leaked browser key cannot wipe data.

Step 1 — verify the request

You should always have your identity check between the email and the delete. The Worker doesn't authenticate the end user; it authenticates you via the sk_* key.

async function forgetUser(userId: string, requestedBy: string) {
  // 1. Confirm the requester is who they say they are (your auth).
  // 2. Log the request in your own audit table.
  await db.insert("forget_requests", {
    user_id: userId,
    requested_by: requestedBy,
    requested_at: new Date()
  });
  // 3. Then, and only then, call Millimetric.
}

Step 2 — call /v1/forget

const res = await fetch(`${process.env.AOA_HOST}/v1/forget`, {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.AOA_SK}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({ user_id: userId })
});

if (!res.ok) {
  const err = await res.json();
  throw new Error(`forget failed: ${err.error}`);
}

return res.json();   // { ok: true, queued: true }

The mutation is queued on ClickHouse — ALTER TABLE events DELETE WHERE project_id = ? AND user_id = ?. Typical completion: seconds. For very large tables: minutes.

/v1/forget only handles Millimetric. Don't forget:

Your application database (the users row, sessions, content).
Stripe / billing provider (use their Customer.delete).
Email provider (Resend / Sendgrid suppression list).
Backups, if you're being thorough — usually documented in your privacy policy as "within X days".

What gets deleted in Millimetric

Every row in events where project_id = <your project> AND user_id = <user>.

What does not get deleted

Thing

Why

Anonymous events from before identify

They have user_id = NULL and are indistinguishable from any other anonymous traffic. By design — the system can't tell which anonymous events belong to a now-known user.

Aggregated rows in daily_rollup and sessions

Aggregates, not personal data. They never had PII. Re-aggregate from raw if you want to strip a user's contribution.

ip_hash rows

Already irreversible. The salt rotates daily, so within a day they're per-user, but cross-day linkability is gone.

Events under other projects

Scoped to the project owning the sk_* key.

If you also need to forget anonymous events

/v1/forget doesn't have anonymous_id support yet (PR welcome). Run the SQL directly against ClickHouse:

ALTER TABLE events DELETE
  WHERE project_id = '{your-project-id}'
    AND anonymous_id = '{the-anonymous-id-the-user-told-you}';

Get the anonymous_id from the user themselves (developer-tools snippet you ship them) or by stitching from user_id first:

SELECT DISTINCT anonymous_id
FROM events
WHERE project_id = '...' AND user_id = 'user_42';

Run forget by user_id first (kills post-identify events), then run the anonymous-id deletes for each one returned.

Audit trail — the part Millimetric doesn't do for you

Today the API doesn't yet write a structured audit row for /v1/forget calls. Until that's built, you keep your own audit log on the calling side:

CREATE TABLE forget_requests (
  id            uuid primary key default gen_random_uuid(),
  user_id       text not null,
  requested_by  text not null,
  requested_at  timestamptz not null,
  millimetric_response jsonb,
  related_systems jsonb default '[]'::jsonb
);

Log:

Who made the request.
Who approved it.
Timestamp.
The exact response from /v1/forget (so you have proof of the queued mutation).
Other systems you also wiped (Stripe customer id, etc.).

Keep this audit log indefinitely — it's your compliance evidence.

Worked example

import { z } from "zod";

const Body = z.object({ user_id: z.string().min(1) });

export async function POST(req: Request) {
  // 1. Authenticate the operator. Probably an admin role on your side.
  const session = await requireAdmin(req);

  // 2. Validate input.
  const { user_id } = Body.parse(await req.json());

  // 3. Audit before action.
  const audit = await db.insert("forget_requests", {
    user_id,
    requested_by: session.userId,
    requested_at: new Date()
  });

  // 4. Millimetric.
  const mmRes = await fetch(`${process.env.AOA_HOST}/v1/forget`, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.AOA_SK}`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({ user_id })
  });
  const mmJson = await mmRes.json();
  await db.update("forget_requests", { id: audit.id }, { millimetric_response: mmJson });

  if (!mmRes.ok) return Response.json(mmJson, { status: 500 });

  // 5. Other systems.
  await stripe.customers.del(stripeCustomerIdFor(user_id));
  await db.delete("users").where("id", user_id);

  return Response.json({ ok: true });
}

Errors

Status

error

Meaning

401

invalid_api_key

sk_* revoked or wrong project.

403

forget_requires_secret_key

You sent a pk_*.

400

invalid_payload

user_id missing or empty.

500

forget_failed

ClickHouse rejected the mutation. Worker logs have the trace. Retry.