Quickstart

• Requirements
• Client-side
• Server-side
  • Token Validation

Requirements

• Server-side library: At least Node 14. Most modern Bun or Deno versions should work too. If you're using Glitch, make sure to set Node 14 or higher in your engines field in package.json. If you don't use a JavaScript runtime, consider using the Standalone server.

• Client-side widget: All modern browsers should be supported. A compatibility version is available too.

Client-side

Start by adding importing the Cap widget library from a CDN:

<script src="https://cdn.jsdelivr.net/npm/@cap.js/widget"></script>

Next, add the <cap-widget> component to your HTML.

<cap-widget
  id="cap"
  data-cap-api-endpoint="<your cap api endpoint>"
></cap-widget>

NOTE

You'll need to start a server with the Cap API running at the same URL as specified in the data-cap-api-endpoint attribute. In the server-side example we provided, it's set to /api, but you can change this by replacing every app.post('/api/...', ...) to app.post('/<endpoint>/...', ...).

Then, in your JavaScript, listen for the solve event to capture the token when generated:

const widget = document.querySelector("#cap");

widget.addEventListener("solve", function (e) {
  const token = e.detail.token;

  // Handle the token as needed
});

Alternatively, you can use onsolve="" directly within the widget or wrap the widget in a <form></form> (where Cap will automatically submit the token alongside other form data).

Server-side

Cap is fully self-hosted, so you'll need to start a server with the Cap API running at the same URL as specified in the data-cap-api-endpoint attribute. This is easy since we've already pre-made a library to help you generate and validate challenges for you.

Start by installing it:

bun

bun add @cap.js/server

npm

npm i @cap.js/server

pnpm

pnpm i @cap.js/server

NOTE

It is recommended to use at least Node.js 14 or Bun 1.0.0. You might experience multiple issues on older versions of these runtimes.

Now, you'll need to change your server code to add the routes that Cap needs to work. Here's an example:

Elysia

import { Elysia } from "elysia";
import Cap from "@cap.js/server";

const cap = new Cap({
  tokens_store_path: ".data/tokensList.json",
});

new Elysia()
  .post("/api/challenge", () => {
    return cap.createChallenge();
  })

  .post("/api/redeem", async ({ body, set }) => {
    const { token, solutions } = body;

    if (!token || !solutions) {
      set.status = 400;
      return { success: false };
    }

    return await cap.redeemChallenge({ token, solutions });
  })
  .listen(3000);

console.log(`🦊 Elysia is running at http://localhost:3000`);

Fastify

import Fastify from "fastify";
import Cap from "@cap.js/server";

const fastify = Fastify();
const cap = new Cap({
  tokens_store_path: ".data/tokensList.json",
});

fastify.post("/api/challenge", (req, res) => {
  res.send(cap.createChallenge());
});

fastify.post("/api/redeem", async (req, res) => {
  const { token, solutions } = req.body;
  if (!token || !solutions) {
    return res.code(400).send({ success: false });
  }

  res.send(await cap.redeemChallenge({ token, solutions }));
});

fastify.listen({ port: 3000, host: "0.0.0.0" }).then(() => {
  console.log("Server is running on http://localhost:3000");
});

Bun.serve

import Cap from "@cap.js/server";

const cap = new Cap({
  tokens_store_path: ".data/tokensList.json",
});

Bun.serve({
  port: 3000,
  routes: {
    "/api/challenge": {
      POST: () => {
        return Response.json(cap.createChallenge());
      },
    },
    "/api/redeem": {
      POST: async (req) => {
        const body = await req.json();
        const { token, solutions } = body;

        if (!token || !solutions) {
          return Response.json({ success: false }, { status: 400 });
        }

        return Response.json(await cap.redeemChallenge({ token, solutions }));
      },
    },
  },
});

console.log(`Server running at http://localhost:3000`);

Express

import express from "express";
import Cap from "@cap.js/server";

const app = express();
app.use(express.json());

const cap = new Cap({
  tokens_store_path: ".data/tokensList.json",
});

app.post("/api/challenge", (req, res) => {
  res.json(cap.createChallenge());
});

app.post("/api/redeem", async (req, res) => {
  const { token, solutions } = req.body;
  if (!token || !solutions) {
    return res.status(400).json({ success: false });
  }
  res.json(await cap.redeemChallenge({ token, solutions }));
});

app.listen(3000, () => {
  console.log("Listening on port 3000");
});

Token Validation

Once the token is generated and captured, you can use it later to validate the user's identity. You can do this by calling await cap.validateToken in your server-side code:

await cap.validateToken("..."); // returns { success: Boolean }

Note that the token will immediately be deleted after this. To prevent this, use await cap.validateToken("...", { keepToken: true }).