Computing the signature
The signature is computed by following the same procedure as for creating the payment form. All the received fields must be included. To compute the signature:
- Take all the fields starting with vads_.
- Sort these fields alphabetically.
- Make sure that all the fields are encoded in UTF-8.
- Concatenate the result with the test or production certificate separating them with a "+".
- Apply the SHA-1 algorithm to obtain the signature value.