Validating the Capture Context

The capture context that you generate is a JSON Web Token (JWT) data object. The JWT is digitally signed using a public key. This confirms the validity of the JWT and that it comes from Cybersource. When you do not have a key in the JWT header, Cybersource recommends that you follow cryptography best practices and validate the capture context signature.

To validate a JWT, you must obtain its public key. This public RSA key is in JSON Web Key (JWK) format. The public key is associated with the capture context on the Cybersource domain.

To get the public key of a capture context from the header of the capture context itself, you must retrieve the key ID associated with the public key and then pass the key ID to the

/flex/v2/public-keys

endpoint:

From the header of the capture context, get the key ID (

kid

{
    "kid": "3g",
    "alg": "RS256"
}

Send a GET request to the

/flex/v2/public-keys

endpoint and include the key ID. For example:

Test:

GET https://apitest.cybersource.com/flex/v2/public-keys/{3g}

Production:

GET https://api.cybersource.com/flex/v2/public-keys/{3g}

Depending on the cryptographic method you use to validate the public key, you might need to convert the key to privacy-enhanced mail (PEM) format.

The resource returns the public key:

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.GvBzyw6JKl3b2PztHb9rZXawx2T817nYqu6goxpe4PsjqBY1qeTo19R-CP_DkJXov9hdJZgdlzlNmRY6yoiziSZnGJdpnZ-pCqIlC06qrpJVEDob3O_efR9L03Gz7F5JlLOiTXSj6nVwC5mRlcP032ytPDEx5TMI9Y0hmBadJYnhEMwQnn_paMm3wLh2v6rfTkaBqd8n6rPvCNrWMOwoMdoTeFxku-

Use this public RSA key to validate the capture context.

Base64 decode the capture context to get the

kid

from its header:

{
    "kid": "3g",
    "alg": "RS256"
}

Send a GET request to retrieve the public key from

/flex/v2/public-keys/3g

{
    "kty":"RSA",    
    "use":"enc",
    "kid":"3g",
    "n":"ir7Nl1Bj8G9rxr3co5v_JLkP3o9UxXZRX1LIZFZeckguEf7Gdt5kGFFfTsymKBesm3Pe
     8o1hwfkq7KmJZEZSuDbiJSZvFBZycK2pEeBjycahw9CqOweM7aKG2F_bhwVHrY4YdKsp
     _cSJe_ZMXFUqYmjk7D0p7clX6CmR1QgMl41Ajb7NHI23uOWL7PyfJQwP1X8HdunE6ZwK
     DNcavqxOW5VuW6nfsGvtygKQxjeHrI-gpyMXF0e_PeVpUIG0KVjmb5-em_Vd2SbyPNme
     nADGJGCmECYMgL5hEvnTuyAybwgVwuM9amyfFqIbRcrAIzclT4jQBeZFwkzZfQF7MgA6QQ",
     "e":"AQAB"
}