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Validating the Server-Side Capture Context {#validate-capture-context-microv2-card}
===================================================================================

The capture context that you generated is a JSON Web Token (JWT) data object. The JWT is digitally signed using a public key. The purpose is to ensure the validity of the JWT and confirm that it comes from `Visa Acceptance Solutions`. When you do not have a key specified locally in the JWT header, you should follow best cryptography practices and validate the capture context signature.  
To validate a JWT, you can obtain its public key. This public RSA key is in JSON Web Key (JWK) format. This public key is associated with the capture context on the `Visa Acceptance Solutions` domain.  
To get the public key of a capture context from the header of the capture context itself, retrieve the key ID associated with the public key. Then, pass the key ID to the `public-keys` endpoint.  
**Example**  
From the header of the capture context, get the key ID (`kid`) as shown in this example:

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

Append the key ID to the endpoint `/flex/v2/public-keys/`**3g**. Then, call this endpoint to get the public key. IMPORTANT

> 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. {#validate-capture-context-microv2-card_d23e59}

Resource
--------

Pass the key ID (kid), that you obtained from the capture context header, as a path parameter, and send a GET request to the `/public-keys` endpoint:

* Test: `https://apitest.visaacceptance.com``/flex/v2/public-keys/`*{kid}*
* Production: `https://api.visaacceptance.com``/flex/v2/public-keys/`*{kid}*

The resource returns the public key. Use this public RSA key to validate the capture context.

Example {#validate-capture-context-microv2-card_validate-capture-context-example}
---------------------------------------------------------------------------------

```
eyJraWQiOiJqNCIsImFsZyI6IlJTMjU2In0.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.G4Ea-gIk6SG5ULE4NE5OsdPI41YaAuTEMHDstBgkFzczIWwzJScvXs4hgWiyA-1ZLGITedlumGj-0x8jxmYTWeTm7D0fP8RL0w148EpDLMD8xMHpAJMdMqZTmYHyichsy8uOZKVOn9NbnuQqfDeQS_rLpJV3tMe2NwJL3RdBXdJ894ihKpFP2yXE1wQeLekNiYJ6s-Uuxwf0jf2CSN_TJAjnfVR6bqlpWbUpiUaBLcqDsHHe_pcrd5g2r-1LEfCiOV9RIw7844XKFNLQZvt_alQjItuMy8M9LVhnlRWCSnTKB1iV1RUxuTWtMzTvHmQWPx4nShqzE3j0Hp61c0PmBw     
```

Parse the JWT capture context to get the key ID (`kid`) from its header:

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

Get its 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"
}
```

Related Information
-------------------

* [*Introduction to JSON Web Tokens*](https://jwt.io/introduction "")
* [IETF RFC 7515: JSON Web Signature (JWS) Signature](https://tools.ietf.org/html/rfc7515 "")
* [IETF RFC 7517: JSON Web Key (JWK)](https://tools.ietf.org/html/rfc7517 "")  
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