EUデジタルIDウォレットへの対応準備を。

# Didit: get ready for the EUDI Wallet with the ID Verification step you run today

You are adding electronic identification to my_stack so the product is ready
for the EU Digital Identity (EUDI) Wallet. Every URL, header and enum value
below is canonical. Do not paraphrase or "improve" them.

## 0. What exists today, and what does not
- EUDI Wallet acceptance on Didit is coming soon. There is NO EUDI-specific
  endpoint, wallet id, field or flag to integrate yet. Do not invent one, do
  not send any EUDI identifier in a workflow, and do not build an OpenID4VP
  verifier yourself as part of this task.
- What is live: national digital ID wallets inside the ID Verification step,
  with document capture (chip reading, liveness, face match) as the fallback.
  EUDI Wallet acceptance is planned for the same ID Verification step, so the
  workflow, session call and webhook you build now are the ones you keep.
- The live wallets, as listed by the methods catalog:
  - MitID: wallet id mitid, country keys DNK (Denmark)
  - BankID: wallet id bankid_se, country keys SWE (Sweden)
  - Finnish Trust Network: wallet id ftn, country keys FIN (Finland)
  - Smart-ID: wallet id smart_id, country keys EST (Estonia), LVA (Latvia), LTU (Lithuania), BEL (Belgium)
  - Mobile-ID: wallet id mobile_id, country keys EST (Estonia), LTU (Lithuania)
  Check the catalog for your environment before you go live. Never
  hard-code dates.

## 1. Provision an account
- Sign up: https://business.didit.me (no credit card required).
- Copy the API key of your application from the console.

## 2. Read the methods catalog
Availability is server-driven per country. Only wallets marked available can
be enabled on a live application.
  - Business Console: your application -> Workflows -> the ID Verification
    step -> Countries -> "Wallets accepted". Coming-soon wallets are listed
    but cannot be switched on. https://docs.didit.me/console/id-verification-methods
  - Didit MCP server (https://mcp.didit.me/mcp), tool
    didit_workflow_get_id_verification_methods_catalog; pass country as ISO
    3166-1 alpha-3 to narrow it. The MCP server signs in with "Log in with
    Didit" (OAuth). It does not accept the x-api-key.
    https://docs.didit.me/integration/mcp/tools
  - Public coverage table (no sign-in, read-only):
    https://docs.didit.me/core-technology/id-verification/digital-id-wallets#supported-wallets
If your code holds only an API key, it cannot read the catalog itself: use the
wallet ids listed in this prompt, and treat the answer of the workflow save as
the check. A live application answers 400 for a wallet that is not available
in that country ("<wallet> is not offered in <ISO3>", "unknown wallet").

## 3. Create the workflow (ID Verification = feature OCR)
POST https://verification.didit.me/v3/workflows/
  -H "x-api-key: <your-api-key>"
  -H "Content-Type: application/json"

{
  "workflow_label": "eID onboarding",
  "features": [
    {
      "feature": "OCR",
      "config": {
        "methods": {
          "DNK": {
            "document": { "enabled": true },
            "wallet": {
              "enabled": true,
              "providers": ["mitid"],
              "on_failure": "fallback_to_document"
            }
          },
          "EST": {
            "document": { "enabled": true },
            "wallet": {
              "enabled": true,
              "providers": ["smart_id", "mobile_id"],
              "on_failure": "fallback_to_document"
            }
          }
        }
      }
    }
  ]
}

Response: 201. The workflow id is uuid (workflow_id carries the same value);
the workflow is published straight away. Create it once and keep the id:
every call to this endpoint makes a new workflow.
is_desktop_allowed defaults to false: on a desktop browser the hosted flow
then shows a QR code to continue on a phone. Add "is_desktop_allowed": true
next to workflow_label to let people finish on desktop.

Rules the API enforces:
  - OCR is UPPERCASE; ID_VERIFICATION is rejected in this body (the decision
    later lists the step as ID_VERIFICATION in its features)
  - country keys are ISO 3166-1 alpha-3; method keys are document, id_lookup, wallet
  - providers is an accept-list, not a ranking; the end user picks
  - on_failure is fallback_to_document or decline
  - a wallet the catalog does not mark available rejects the whole save (400)
  - every other country keeps document capture, so people without an eID
    can still verify
  - this body runs document capture only. Chip reading, liveness and face
    match are their own features: add { "feature": "NFC" },
    { "feature": "LIVENESS" } and { "feature": "FACE_MATCH" } to features
    when your policy needs them

## 4. Create a session
POST https://verification.didit.me/v3/session/
  -H "x-api-key: <your-api-key>"
  -H "Content-Type: application/json"
  -d '{ "workflow_id": "<id from step 3>", "vendor_data": "<your user id>" }'

Response: 201 with session_id, session_token, url and status "Not Started".
Redirect the user to url (hosted flow) or open it in the Web, iOS, Android,
React Native or Flutter SDK. The field is named url on this response.
One unfinished session exists per workflow_id and vendor_data pair: calling
create again with the same pair answers 201 again with that same session.

## 5. Webhook
Register a destination in the console (API & Webhooks), or over the API:

POST https://verification.didit.me/v3/webhook/destinations/
  -H "x-api-key: <your-api-key>"
  -H "Content-Type: application/json"
  -d '{
    "label": "Verification webhooks",
    "url": "https://<your-public-host>/webhooks/didit",
    "webhook_version": "v3",
    "subscribed_events": ["status.updated", "data.updated"]
  }'

label, url and subscribed_events are required. url must be a public HTTPS
address: Didit does not deliver to localhost or private addresses. Response:
201 with uuid and secret_shared_key. Store secret_shared_key as the webhook
secret (DIDIT_WEBHOOK_SECRET); it is unique to this destination. Remove a
destination with DELETE /v3/webhook/destinations/{uuid}/ (204).

What arrives:
  - webhook_type is "status.updated" (the session changed status) or
    "data.updated" (verification data was corrected after the fact)
  - a destination receives the events of every session of the application,
    so filter on workflow_id or vendor_data when several flows share it
  - creating a session already sends status.updated with status
    "Not Started". The decision key is present only when status is Approved,
    Declined, In Review or Abandoned.

Verify every delivery:

  Header:      X-Signature-V2 (not X-Signature, not X-Signature-Simple)
  Algorithm:   HMAC-SHA256, hex digest, over the canonical JSON of the payload
               (Python json.dumps(sort_keys=True, separators=(",", ":"),
               ensure_ascii=False) after whole-valued floats become ints).
               Never hash the raw request bytes under this header.
  Freshness:   the signed body field timestamp is the dispatch time (Unix
               seconds). Reject when abs(now - timestamp) > 300 seconds, and
               reject when the X-Timestamp header does not equal it.
  Idempotency: event_id is the same on every retry of one event, so store it
               and skip a delivery you already processed. One session can
               still send the same status under two event ids, and the
               console's Try Webhook test deliveries carry no event_id, so
               also make the handler safe to run twice for one
               (session_id, status, webhook_type).
  Compare:     constant-time (crypto.timingSafeEqual)

Reference handler (Express). Keep the verification lines as written.
The handler is a fragment. Put this above it and app.listen(process.env.PORT)
below it. It needs Express and Node 21 or newer (an older Node rejects
every delivery). It expects a JSON body: answer 400 yourself if you accept
anything else on this route, and refuse to start without the secret.

const express = require("express");
const app = express();
const SECRET = process.env.DIDIT_WEBHOOK_SECRET; // secret_shared_key of the destination

// Your endpoint receives a signed payload
const crypto = require("node:crypto"); // ESM: import crypto from "node:crypto"
// X-Signature-V2 = HMAC over the canonical JSON, never the raw bytes. Match the sender byte for
// byte: keys sorted by code point, integers digit for digit, floats in Python's repr.
class Num { constructor(src) { this.src = src; } } // a number as written on the wire, not a double
const num = (s) => { if (/^-?\d+$/.test(s)) return BigInt(s).toString(); const n = +s; // ints stay exact
  if (Number.isInteger(n)) return BigInt(n).toString(); const [m, e] = n.toExponential().split("e"); // 27.0 -> 27
  return +e >= -4 ? String(n) : `${m}e-${String(-e).padStart(2, "0")}`; }; // 1e-05, not 0.00001
const byCodePoint = (a, b) => Buffer.compare(Buffer.from(a), Buffer.from(b)); // UTF-8 order = Python's
const canon = (v) => Array.isArray(v) ? `[${v.map(canon)}]` : v instanceof Num ? num(v.src)
  : v && typeof v === "object" ? `{${Object.keys(v).sort(byCodePoint).map((k) => `${JSON.stringify(k)}:${canon(v[k])}`)}}`
  : JSON.stringify(v);
// Read the body as text: express.json() would round 1000000000000000129 to a double first.
// Register this route ABOVE any global app.use(express.json()): the first parser to run
// consumes the stream, and a body it already parsed has lost the digits the signature covers.
app.post("/webhooks/didit", express.text({ type: "application/json" }), (req, res) => {
  const exact = JSON.parse(req.body, (k, v, c) => typeof v === "number" ? new Num(c.source) : v); // Node 21+
  const body = JSON.parse(req.body);
  const mac = crypto.createHmac("sha256", SECRET).update(canon(exact), "utf8").digest("hex");
  const sig = Buffer.from(String(req.headers["x-signature-v2"] ?? ""));
  // Freshness comes from the signed body timestamp; the header alone is unsigned and replayable.
  const ts = body.timestamp, fresh = String(ts) === req.headers["x-timestamp"]
    && Math.abs(Date.now() / 1000 - ts) <= 300;
  if (!fresh || sig.length !== mac.length
    || !crypto.timingSafeEqual(sig, Buffer.from(mac))) return res.sendStatus(401);
  const { status, decision } = body;
  // One entry per ID Verification node; pick yours by node_id when you run several.
  const [idv] = decision?.id_verifications ?? [];
  // idv.verification_method: "document" | "id_lookup" | "wallet"
  res.sendStatus(200);
});

Status values (exact strings): Not Started, In Progress, Approved, Declined,
In Review, Resubmitted, Expired, Abandoned, Kyc Expired. Awaiting User only
appears on business verification sessions.

## 6. Read the result
The same V3 decision reaches you two ways:
  - webhook body: body.decision.id_verifications[]
  - GET https://verification.didit.me/v3/session/{session_id}/decision/
      -H "x-api-key: <your-api-key>"
    This response IS the decision object. Read id_verifications at the top
    level: there is no decision wrapper here.
Until the user finishes the ID step, status is "Not Started" or "In Progress"
and id_verifications is null, not an empty array. Guard for it.

id_verifications[] has one entry per ID Verification node; with a single step
take index 0. A wallet sign-in sets:
  verification_method    "wallet"
  assurance              "cryptographic"
  wallet_provider        the catalog wallet id the user picked
  wallet_verification    provider, provider_name, issuing_authority,
                         issuing_country, credential_type, level_of_assurance,
                         verified_at, signature_valid, attributes, portrait
                         (null for the live wallets), face_match_score
  fallback_from          { method, reason, action } when the wallet sign-in failed
                         and on_failure declined the session; otherwise
                         null. After a document fallback that succeeds the
                         entry reads verification_method "document" with
                         fallback_from null
  full_name,             the normalised identity fields, on the entry itself
  date_of_birth
On a live application, check wallet_verification.signature_valid before you
trust attributes. The
live wallets return name, date of birth and a scheme identifier (for example
the Swedish personnummer; MitID returns a pseudonymised identifier), never an
address or a portrait: collect those through other steps if your policy
needs them.
Reference: https://docs.didit.me/core-technology/id-verification/digital-id-wallets

## 7. Billing
Only completed wallet sign-ins are billed; cancelled, timed-out and failed
ones are free. Prices per wallet: https://didit.me/pricing

## 8. Verify your integration
Sandbox (an application in sandbox mode: nothing is billed and no real eID is
called). https://docs.didit.me/integration/sandbox-testing
  - a sandbox application can enable every wallet in the catalog, the
    coming-soon ones included. A workflow that saves in sandbox can still be
    refused on a live application, so only use wallets marked available.
  - open the session url, pick the wallet and confirm: the default approve
    scenario simulates the sign-in. The entry then has verification_method
    "wallet", assurance "cryptographic" and wallet_provider set, and the
    normalised full_name and date_of_birth are filled. But
    wallet_verification.signature_valid and level_of_assurance are null and
    attributes is { "sandbox": true }: no real credential was checked.
    Assert signature_valid === true and the level of assurance only against
    a live application.
  - to exercise on_failure, create the session with
    "sandbox_scenario": "wallet_cancelled" (also wallet_timeout and
    wallet_provider_error). The wallet sign-in then fails and the flow moves
    to document capture or declines, as on_failure says. A fallback that
    ends in an approved document reads verification_method "document".
  - POST /v3/session/{session_id}/simulate/ forces a final status but writes
    no id_verifications entry, so it cannot stand in for a sign-in.

Checks:
  - create the workflow, create a session, and read its decision: expect 201,
    201 with url, and 200 with status "Not Started"
  - run one sandbox session per accepted wallet through the hosted flow and
    assert verification_method is "wallet" and wallet_provider is the wallet
    you picked
  - run one session with sandbox_scenario "wallet_cancelled" and assert the
    flow offers document capture
  - assert the webhook accepts a correctly signed payload and rejects a wrong
    X-Signature-V2, a changed body, and a payload whose signed timestamp is
    older than 300 seconds, even when X-Timestamp is refreshed
  - on a live application, assert wallet_verification.signature_valid is true

Docs: https://docs.didit.me/core-technology/id-verification/digital-id-wallets