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Server-side validation

Customers must call the siteverify endpoint to validate the Turnstile widget response from their website’s backend. The widget response must only be considered valid once it has been verified by the siteverify endpoint. The presence of a response alone is not enough to verify it as it does not protect from replay or forgery attacks. In some cases, Turnstile may purposely create invalid responses that are rejected by the siteverify API.

Tokens issued to Turnstile using the success callbacks, via explicit or implicit rendering, must be validated using the siteverify endpoint.

The siteverify endpoint needs to be passed a secret key that is associated with the sitekey. The secret key will be provisioned alongside the sitekey when you create a widget.

Furthermore, the response needs to be passed to the siteverify endpoint.

Example using cURL:

$ curl 'https://challenges.cloudflare.com/turnstile/v0/siteverify' --data 'secret=verysecret&response=<RESPONSE>'
{
"success": true,
"error-codes": [],
"challenge_ts": "2022-10-06T00:07:23.274Z",
"hostname": "example.com"
}

Example using fetch from Cloudflare Workers:

// This is the demo secret key. In production, we recommend
// you store your secret key(s) safely.
const SECRET_KEY = '1x0000000000000000000000000000000AA';
async function handlePost(request) {
const body = await request.formData();
// Turnstile injects a token in "cf-turnstile-response".
const token = body.get('cf-turnstile-response');
const ip = request.headers.get('CF-Connecting-IP');
// Validate the token by calling the
// "/siteverify" API endpoint.
let formData = new FormData();
formData.append('secret', SECRET_KEY);
formData.append('response', token);
formData.append('remoteip', ip);
const url = 'https://challenges.cloudflare.com/turnstile/v0/siteverify';
const result = await fetch(url, {
body: formData,
method: 'POST',
});
const outcome = await result.json();
if (outcome.success) {
// ...
}
}

Check out the full demo on GitHub.

​​ Accepted parameters

POST ParameterRequired/OptionalDescription
secretRequiredThe site’s secret key.
responseRequiredThe response provided by the Turnstile client-side render on your site.
remoteipOptionalThe user’s IP address.

The siteverify endpoint behaves similar to reCAPTCHA’s siteverify endpoint. The response type of the siteverify is application/json.

It always contains a ‘success’ property, either true or false, indicating whether the operation was successful or not.

In case of a successful validation, the response should be similar to the following:

{
"success": true,
"challenge_ts": "2022-02-28T15:14:30.096Z",
"hostname": "example.com",
"error-codes": [],
"action": "login",
"cdata": "sessionid-123456789"
}
  • challenge_ts is the ISO timestamp for the time the challenge was solved.
  • hostname is the hostname for which the challenge was served.
  • action is the customer widget identifier passed to the widget on the client side. This is used to differentiate widgets using the same sitekey in analytics. Its integrity is protected by modifications from an attacker. It is recommended to validate that the action matches an expected value.
  • cdata is the customer data passed to the widget on the client side. This can be used by the customer to convey state. It is integrity protected by modifications from an attacker.
  • error-codes is a list of errors that occurred.

In case of a validation failure, the response should be similar to the following:

{
"success": false,
"error-codes": [
"invalid-input-response"
]
}

A validation error is indicated by having the success property set to false. A list of error codes is provided to indicate why a response has failed to verify. The response may also contain additional fields based on whether Turnstile siteverify was able to parse the response successfully or unsuccessfully.

​​ Error codes

Error codeDescription
missing-input-secretThe secret parameter was not passed.
invalid-input-secretThe secret parameter was invalid or did not exist.
missing-input-responseThe response parameter was not passed.
invalid-input-responseThe response parameter is invalid or has expired.
bad-requestThe request was rejected because it was malformed.
timeout-or-duplicateThe response parameter has already been validated before.
internal-errorAn internal error happened while validating the response. The request can be retried.