# Computing the digest

The signed **Authorization** header includes, among other claims, a sha256 digest of the HTTP request (note: the Finqware API only uses POST application/json requests similar to a GraphQL API).

#### Steps

1. take the json payload and compress it to a single-line json without any whitespaces
   * make sure you do not remove any useful whitespaces (eg: from a debtor name when submitting a payment)
   * it is recommended to use a standard json library to do that instead of your own regex

     ```python
     #
     # Python example
     #

     http_payload = {
       "client_id": "51e2389....02d51",
       "client_app_key": "MDAxNmxvY2F0aWMz...D9rgv7_DySaiYgo", 
       "skill": "bt_ro_aisp_sbx_#2.0"
     }

     # a compact stringified json without any whitespaces 
     compact_http_payload = json.dumps(http_payload, separators=(',', ':')).encode("utf-8")
     ```
2. compute a Base64 (not URL-safe) encoded SHA-256 hash of the compressed json format

   ```python
   digest = hashlib.sha256(compact_http_payload).digest()
   b64_digest = base64.b64encode(digest).decode("utf-8")
   ```

***Note***:

* make sure your HTTP client sends the request with the json keys in the same order as in the payload used when computing the digest


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