Example: Notfallkarte¶

Notfallkarte (German for emergency card) is a small web page on which a bank-card-sized card for the wallet is made. The card carries a name and a QR code. Whoever scans it in an emergency sees the emergency contact, allergies, medication and doctor as the vault holds them today, not as they were when the card was printed. A change in the vault shows on the card straight away, and once the link is revoked, the card leads nowhere.

It is a complete link proposal tool and serves as the reference for building others: a static page without an account, without a backend and without access to the vault. Its source lives in its own notfallkarte repository.

The flow, step by step¶

1. On the card page, the name for the card is entered and the groups a helper should see are ticked. Insurance and organ donation start unticked, since anyone holding the card can read what it leads to.

2. Continue in revoked opens a proposal link in the installed app. It names the card and a list of record keys, never a value (wrapped here for reading):

   revoked://p?label=Notfallkarte%20Max%20Mustermann
     &keys=full_name,contact_name,contact_phone,contact_relation,blood_type,allergies,medications,doctor_name,doctor_phone
     &from=Notfallkarte
     &template=Medical%20emergency%20card
   

Without the app installed, the link opens nothing. The page notices that nothing took over and says so, with a link to get revoked. After installing, Open Revoked is pressed once more: the card is still in the list, and the app carries the proposal through sign-up and workspace setup and opens it once they are done.

1. In the app, the share it would create is shown. The keys belong to the built-in Medical emergency card template, so anything the vault does not hold yet is asked for once, with the right label. The proposal sets no expiry, since a card has to work on the day it is needed.
2. After confirmation, the share is created on the owner's own server, by the app.
3. The link returns to the card page — either automatically, when the page is connected and allowed to receive links, or by being copied in the app and pasted into the page. The QR code is drawn from it, and the card is offered as a PNG (300 dpi) or as an A4 print sheet at true size.

Once connected, the page also shows the status of each card — active, opened N×, paused, revoked — and, where that was allowed, the link is revoked when a card is removed. Cards are found again in another browser through the link's label and the page's own reference (<card id>.<groups>), which was set on the proposal. Nothing is kept on the server for the page, and its own storage holds no more than names and ticked groups.

Who knows what¶

The card itself is the credential: the link opens the data, which is the whole point of an emergency card. The groups are best chosen with that in mind. A lost card is dealt with by revoking its link; a new card with a new link takes about a minute.

Self-hosting¶

The page consists of static files and only talks to the server the app names on the way back, so a single deployment works with every revoked server:

cd notfallkarte
cp .env.example .env
docker compose up -d --build

Like the revoked stack, the compose file publishes no port and joins the reverse proxy's network (proxy-network by default). The proxy points at notfallkarte:8080 under a host name of its own, for example notfallkarte.example.com. A revoked server running with a restricted --origins list needs the card page's origin added to it, since the page calls the server from the browser once connected. REVOKED_DOWNLOAD_URL in .env sets where Get Revoked leads (https only; empty means revoked's latest release).

How a tool like this is put together, including a minimal working page, is described in Building a tool.