Verify HMAC signatures

To protect your server from unauthorised webhook events, we strongly recommend that you use Hash-based message authentication code (HMAC) signatures for our webhooks that support it. For the ones that support enabling HMAC signatures, each webhook event will include a signature calculated using a secret HMAC key and a payload from the webhook. By verifying this signature, you confirm that the webhook was sent by Adyen, and was not modified during transmission.

To verify HMAC signatures, you can either:

• Use one of our libraries.
• Build your own custom solution.

Enable HMAC signatures

Each secret HMAC key is linked to one webhook endpoint. If you have multiple endpoints for receiving webhooks, generate an HMAC key for each of them.

To start receiving HMAC signed webhooks, if the option is available:

1. In your Customer Area, go to Developers > Webhooks.
2. From the list of webhooks, select the one to configure.
3. Select Edit webhook or the edit icon .
4. Under Security, generate a new HMAC key or enter an existing HMAC key.
   If you generate a new HMAC key, copy it and store it securely in your system.
5. Select Save configuration.

The HMAC key will now be used to sign webhook events that we send to your server.

For our Standard webhooks, the signature is included in the additionalData field.

For other types of webhooks, although rare, the signature can be included in the request header. When the HMAC signature is included in the header, the steps to follow to verify the signature is different. See Verify HMAC keys returned in the header.

{
   "live":"false",
   "notificationItems":[
      {
         "NotificationRequestItem":{
            "additionalData":{
               "hmacSignature":"+JWKfq4ynALK+FFzGgHnp1jSMQJMBJeb87dlph24sXw="
            },
          ...
         }
      }
   ]
}

Verify using our libraries

You can verify signatures using our:

• Java library
• PHP library
• C# library
• JavaScript library
• Ruby Library
• Python Library

Verify using your own solution

To build your own solution for verifying HMAC signatures, follow these steps:

Step 1: Construct the payload

Concatenate the following values from the webhook event, in the given order:

Assign an empty string to any fields that are empty, and use a colon (":") to delimit the values.

For the above values, with an empty originalReference, you get:

7914073381342284::TestMerchant:TestPayment-1407325143704:1130:EUR:AUTHORISATION:true

Step 2: Calculate the HMAC signature

1. Convert the payload that you constructed to a binary representation, given the UTF-8 charset.

2. Convert the hexadecimal HMAC key that you generated in your Customer Area from a hexadecimal string to a binary representation, given the UTF-8 charset.

3. Calculate an HMAC using:

   • The SHA256 function.
   • The binary representation of the payload.
   • The binary representation of the HMAC key.

4. To get the final signature, Base64-encode the result.

Step 3: Compare signatures

If the signature that you calculated in Step 2 matches the hmacSignature that you received, you'll know that the webhook event was sent by Adyen and was not modified during transmission.

Example

Sample HMAC key:

44782DEF547AAA06C910C43932B1EB0C71FC68D9D0C057550C48EC2ACF6BA056

Sample webhook event signed using the above HMAC key:

{
   "live":"false",
   "notificationItems":[
      {
         "NotificationRequestItem":{
            "additionalData":{
               "hmacSignature":"coqCmt/IZ4E3CzPvMY8zTjQVL5hYJUiBRg8UU+iCWo0="
            },
            "amount":{
               "value":1130,
               "currency":"EUR"
            },
            "pspReference":"7914073381342284",
            "eventCode":"AUTHORISATION",
            "eventDate":"2019-05-06T17:15:34.121+02:00",
            "merchantAccountCode":"TestMerchant",
            "operations":[
               "CANCEL",
               "CAPTURE",
               "REFUND"
            ],
            "merchantReference":"TestPayment-1407325143704",
            "paymentMethod":"visa",
            "success":"true"
         }
      }
   ]
}

Verify HMAC keys returned in the header

For non-standard webhooks, Adyen can sign the webhook with an HMAC signature in the request header, instead of including it in the additionalData field. If you enabled other webhooks that follow this pattern, for example, the Recurring tokens life cycle events webhook, there are different steps to verify the HMAC signature.

1. For every webhook that you receive, get the values from the following headers:

   • hmacsignature: Contains the signature.
   • protocol: The protocol used to create the signature, HmacSHA256.

2. Calculate the signature using:

   • SHA256.
   • The binary representation of the payload.
   • The binary representation of the HMAC key.
   • Make sure that the request body is as it is—do not deserialize it.

3. To get the final signature, Base64-encode the result.

4. Compare the hmacsignature received from the header and the calculated signature. If the signatures match, then the webhook was sent by Adyen and was not modified during transmission.

Below is an examples HMAC signature validation.

See also