Fastify CAPTCHA Integration

This recipe shows how to integrate TrustCaptcha into a Fastify application. The frontend setup is the same as for any other Node.js application — this page focuses on the server-side validation.

The setup section gets you to a working integration in three small steps using a route handler directly. Below it, an optional refactor section shows the more reusable Fastify-idiomatic approach (a preHandler hook).

You should have already completed the following steps before you wire TrustCaptcha into your Fastify application.

1. Read Get-Started: Get a quick overview of the concepts behind TrustCaptcha and the integration process in get started.

2. Existing CAPTCHA: If you don’t have a CAPTCHA yet, sign in or create a new user account. Then create a new CAPTCHA.

First, add the TrustCaptcha script to your page (see the JavaScript Guide for version pinning and self-hosting options).

Then place the <trustcaptcha-component> element inside your form. The widget appends a hidden tc-verification-token field on submit, which your Fastify route receives like any other form input.

<script type="module" src="https://cdn.trustcomponent.com/trustcaptcha/3.0.x/trustcaptcha.esm.min.js"></script>

<form method="post" action="/contact">
    <label>Email</label>
    <input type="email" name="email" required>

    <trustcaptcha-component sitekey="<your_site_key>"></trustcaptcha-component>

    <button type="submit">Send</button>
</form>

See the Widget Overview for the full property reference.

npm i fastify @fastify/formbody @trustcomponent/trustcaptcha-nodejs@^3.0.0

import Fastify from "fastify";
import formbody from "@fastify/formbody";
import { TrustCaptcha } from "@trustcomponent/trustcaptcha-nodejs";

const fastify = Fastify({ logger: true });
await fastify.register(formbody);

fastify.post("/contact", async (request, reply) => {
    // In production, load from env: process.env.TRUSTCAPTCHA_API_KEY
    const apiKey = "<your_api_key>";
    const body = request.body as Record<string, string>;
    const token = body["tc-verification-token"] ?? "";

    try {
        const result = await TrustCaptcha.getVerificationResult(apiKey, token);
        if (!result.verificationPassed || result.score > 0.5) {
            return reply.code(400).send("CAPTCHA verification failed.");
        }
    } catch (err) {
        return reply.code(400).send("CAPTCHA verification failed.");
    }

    // CAPTCHA passed — request data is safe to use.
    // ... your business logic ...

    return reply.send("Thanks!");
});

await fastify.listen({ port: 8080 });

That’s it — the form is now protected. For real deployments, move the API key out of the source code (see the comment) and consider explicit failover handling — see Failover Behavior for the reasoning and a code template.

If you protect more than one route, the most idiomatic Fastify approach is a preHandler hook — Fastify’s per-route middleware equivalent. The verification call then runs automatically before any handler that opts in.

TRUSTCAPTCHA_API_KEY=<your_api_key>

import type { FastifyRequest, FastifyReply } from "fastify";
import { TrustCaptcha } from "@trustcomponent/trustcaptcha-nodejs";

export async function verifyTrustCaptcha(request: FastifyRequest, reply: FastifyReply) {
    const body = request.body as Record<string, string> | undefined;
    const token = body?.["tc-verification-token"] ?? "";
    if (!token) return reply.code(400).send("CAPTCHA verification failed.");

    try {
        const result = await TrustCaptcha.getVerificationResult(
            process.env.TRUSTCAPTCHA_API_KEY!,
            token,
        );
        if (!result.verificationPassed || result.score > 0.5) {
            return reply.code(400).send("CAPTCHA verification failed.");
        }
    } catch (err) {
        return reply.code(400).send("CAPTCHA verification failed.");
    }
}

Per route via preHandler:

import { verifyTrustCaptcha } from "./hooks/trust-captcha";

fastify.post(
    "/contact",
    { preHandler: verifyTrustCaptcha },
    async (request, reply) => {
        // CAPTCHA already verified — body is safe to use.
        return reply.send("Thanks!");
    },
);

Or registered as a plugin scoped to a route prefix:

fastify.register(async (instance) => {
    instance.addHook("preHandler", verifyTrustCaptcha);
    instance.post("/contact",   async (req, reply) => reply.send("Thanks!"));
    instance.post("/newsletter", async (req, reply) => reply.send("Subscribed!"));
}, { prefix: "/forms" });

Body parser. Fastify’s built-in body parsing handles JSON automatically. For application/x-www-form-urlencoded (what the widget posts via standard form submit), register @fastify/formbody as shown above — otherwise request.body is undefined for form posts.

Schema validation. If you use Fastify’s built-in JSON Schema validation on the request body, declare tc-verification-token in the schema (or set additionalProperties: true) so it doesn’t get stripped before your hook runs.

Singleton SDK instance. For configured usage (custom timeouts, proxy, custom API host), construct a single TrustCaptcha instance once at startup with new TrustCaptcha({ apiKey, ... }) (e.g. attach it via fastify.decorate("trustCaptcha", ...) and read it inside the hook) instead of using the static shortcut. See the Node.js Guide for the constructor options.

Once you have wired TrustCaptcha into your Fastify application, you can use TrustCaptcha to its full extent. However, we still recommend the following additional technical and organizational measures:

• Security rules: You can find many security settings for your CAPTCHA in the CAPTCHA settings. These include, for example, authorized websites, CAPTCHA bypass for specific IP addresses, bypass keys, IP based blocking, geoblocking, individual difficulty and duration of the CAPTCHA, and much more. Learn more about the security rules.

• Privacy & GDPR compliance: Include a passage in your privacy policy that refers to the use of TrustCaptcha. We also recommend that you enter into a data processing agreement with us to stay GDPR-compliant. Learn more about data protection.

• Accessibility & UX: Customize TrustCaptcha to your website so that your website is as accessible as possible and offers the best possible user experience. More about accessibility.

• Failover behavior: Decide how your backend should behave when our service is temporarily unreachable. This is particularly important for high-availability flows where blocking real users during an outage is worse than letting through a small amount of unverified traffic. Learn more about failover behavior.

• Testing: If you use automated testing, make sure that the CAPTCHA does not block it. Learn more about testing.