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Work with JSON Web Signatures

Work with JSON Web Signatures

This short guide shows how to create a JSON Web Signature (JWS) when working with our Open Banking API.

JSON Web Signatures (JWSs) are required in several steps when working with all the Payment initiation endpoints. They are used to validate authenticity and integrity of the content of an API request or response.

JWSs are similar to JSON Web Tokens (JWTs), as they both consist of a header, a payload and a cryptographic signature, separated by a dot ..

The JWSs in Open Banking are a special case, because the payload section is omitted. This is because it is already present in the payload of the API request or response.


To work with JWSs, you must first prepare:

  • A signing key and signing certificate pair
  • A JWKs URL at which your JSON Web Key (JWK) is publicly available
  • A JWS library to cryptographically create a JSON Web Signature

To learn how to obtain them for testing purposes, see Get Started: Prepare your Sandbox environment.


Your JWK must contain the x5c parameter populated with the signing certificate corresponding to the kid you will be using.

If you fail to include it, we won't be able to validate your JWS.

The header section of the JWS contains mandatory parameters to validate the signature of payment requests.

You must provide the kid parameter of your signing certificate and the root domain of the URL where your JWK is hosted.

typType, always JOSE (JSON Object Signing and Encryption)
algAlgorithm used for signature, always PS256
kidThe kid parameter of your signing key/certificate
critCritical parameters, must include root domain of your JWKs URL

This is a template JWS header that you can copy and fill with your own kid value and JWKs URL root domain:

"typ": "JOSE",
"alg": "PS256",
"kid": "<kid parameter of your signing certificate>",
"crit": [""],
"": "<root domain of your JWKs URL>"


In the case of JWS, the payload will be the JSON payload of the API request.

For demonstration purposes, in this guide we are using this sample JSON payload:

"test": "payload"

The signature in a JWS is unique for the provided header and payload. Since the payload is provided separately in the request body, you must make sure that its formatting is exactly the same as of the content that was signed.

This is especially important because signing libraries can remove whitespaces and line breaks from the payload before signing, and thus alter the formatting.


To compute the signature, you can use any library that is compatible with your environment.

For example, in JavaScript, a library such as jsrsasign can be used.

private_key = "---abc---";

header = {
"typ": "JOSE",
"alg": "PS256",
"kid": "abc123",
"crit": [""],
"": ""

payload = {
"test": "payload"

sJWS = KJUR.jws.JWS.sign("PS256", header, payload, private_key);

Full Request with JWS

The final JWS for the above header and payload would result in:


The payload section above was bolded to highlight the three sections composing a JWS and facilitate reading.


At this stage you can inspect what exactly is being signed. If you take the payload section (ewogICJ0ZXN0IjogInBheWxvYWQiCn0) and base64-decode it into a string, you will get the payload. Check that it matches exactly the payload in your API request.

To avoid sending redundant data, the payload is then removed from the JWS, leaving only the header and signature with an empty payload section:


For Open Banking API requests that require a JSON Web signature, this string must be included in the x-jws-signature header, as in the example below:


For the signature section of the JWS, we have used an arbitrary string here.

curl --location '' \
--header 'x-fapi-financial-id: 001580000103UAvAAM' \
--header 'Authorization: Bearer oa_prod_pwDmU5mA2QOFvxcWszVP06uhI2nIcOAsgC4iuwlzTiw' \
--header 'Content-Type: application/json' \
--header 'x-jws-signature: ewogICJ0eXAiOiAiSk9TRSIsCiAgImFsZyI6ICJQUzI1NiIsCiAgImtpZCI6ICJhYmMxMjMiLAogICJjcml0IjogWyJodHRwOi8vb3BlbmJhbmtpbmcub3JnLnVrL3RhbiJdLAogICJodHRwOi8vb3BlbmJhbmtpbmcub3JnLnVrL3RhbiI6ICJleGFtcGxlLmNvbSIKfQ..M-tx9BIPmHO8_VpGVmO3yDq--------dFtS6VgiM1kmQuK6E_3S8tKh2BKV_W69Q' \
--header 'x-idempotency-key: 048d46a1-f381-4f2b-a79e-a43ee7d1ff90' \
--data '{
"test": "payload"

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