Sign your payment requests

When you sign your requests to our APIs, you ensure a second layer of security on top of the authorisation bearer token, guaranteeing that the payload has not been tampered with.

All modification requests (for example, POST, DELETE) to our Payments APIs, authenticated with a client_credentials token generated by TrueLayer's authentication server, must also be signed by including a valid Tl-Signature HTTP header.

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Supported algorithms

We only support the ES512 signing algorithm for modification requests to our Payments APIs.

ES512 belongs to the family of Elliptic Curve Digital Signature Algorithms (ECDSA).

To sign an HTTP request using ECDSA you will need to generate an Elliptic Curve (EC) key pair. You will need:

• a public key, to be uploaded in the new Payments Settings page in our Console.
• a private key, to be used for signing requests, which you should not share with anyone outside of your organisation. ES512, in particular, requires a key pair that uses the P-521 family of elliptic curves (also known as secpt521r1).

Generate a signing key pair

You can generate a key pair with OpenSSL on Windows or LibreSSL on macOS or Linux.

To check the version currently installed on your device, run this command in your terminal:

openssl version

If you do not have either the OpenSSL or LibreSSL library installed on your device, install the latest version from the official website.

1. To generate the private key, run the following command in your terminal:

openssl ecparam -genkey -name secp521r1 -noout -out ec512-private-key.pem

2. Then, to generate the public key, run the following command in your terminal:

openssl ec -in ec512-private-key.pem -pubout -out ec512-public-key.pem

3. Go to Console > Payments Settings and upload your public key, the file ec512-public-key.pem.

Sign your requests with our libraries

In our Github, we maintain libraries in a range of languages. These provide methods for signing and verifying according to the scheme described later. Our backend libraries also make use of these signing libraries for the API requests.

E.g. Java com.truelayer.truelayer-signing

// `Tl-Signature` value to send with the request.
String tlSignature = Signer.from(kid, privateKey)
        .header("Idempotency-Key", idempotencyKey)
        .method("post")
        .path(path)
        .body(body)
        .sign();

Sign your requests without using libraries

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Manual signing

We encourage the use of our signing libraries mentioned previously for easier integration.

To manually generate Tl-Signature headers, or verify webhook signatures, it’s still recommended to refer to our Github reference implementations & examples.

In particular see the document describing the signing scheme.

Test your signing logic

You can send a POST or DELETE request to our /test-signature endpoint to verify that you have correctly implemented request signing. The /test-signature endpoint will validate your Tl-Signature header and return a 204 No Content in case of success. It does not perform any kind of validation on the body schema.

curl -X POST \
    -H "Authorization: Bearer ${access_token}" \
    -H "Tl-Signature: ${signature}" \
    --data '{"nonce":"9f952b2e-1675-4be8-bb39-6f4343803c2f"}' \
    https://api.truelayer-sandbox.com/test-signature

Troubleshooting

• Ensure the path you are signing is the same path you are sending the request. So if testing against https://api.truelayer-sandbox.com/test-signature the path should be /test-signature.
  
• Ensure all headers that are being signed are being sent with the request exactly as they were signed and none are missing. So if you sign Idempotency-Key you must also send exactly the same value in the request. Note: /test-signature does not require any headers, so it is possible to test request signing without signing headers here (though headers are required for other endpoints).
  
• Ensure the body passed to the signing library exactly byte-for-byte matches the body sent with the request. It must not be formatted differently or have fields in a different order. Ensure the request body has no trailing newlines if it was not signed that way.
  
• Ensure the KID and private key you are signing with match the KID in our Console & public key that was uploaded there.
  
• Try testing the endpoints using Insomnia + insomnia-plugin-jws-by-truelayer plugin. The plugin generates Tl-Signature headers using the private key and KID environment variables, so can be used to check that the keys and Console configuration are correct.

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Import our Insomnia collection