Callback Request Signing

The Sinch Platform can initiate callback requests to a URL you define (Callback URL) on request and result events. All callback requests are signed using your Application key and secret pair found on your dashboard. The signature is included in the Authorization header of the request.

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    Authorization = "Application" + " " + ApplicationKey + ":" + Signature

    Signature = Base64 ( HMAC-SHA256 ( Base64-Decode( ApplicationSecret ), UTF8 ( StringToSign ) ) );

    StringToSign = HTTP-Verb + "\n" +
        Request-Body-Content-MD5 + "\n" +
        Request-Content-Type + "\n" +
        Request-CanonicalizedHeaders + "\n" +
        Request-CanonicalizedResource;

    Request-Body-Content-MD5 = Base64 ( MD5 ( [REQUEST-BODY] ) )

Pseudocode Component	Description
`Request-CanonicalizedHeaders`	The only required header is `x-timestamp`.
`Request-CanonicalizedResource`	The path to the API resource. For example, `verification/v1/verifications`.
`ApplicationKey`	The key for your Voice application found on your dashboard.
`ApplicationSecret`	The secret for your Voice application found on your dashboard. Important!: The Application Secret value must be base64-decoded from before it's used for signing.

Timestamp

Sinch sends a custom request header x-timestamp (time) with each request that can be validated by your server. This custom header is used to determine that the request is not too old. The timestamp is also part of the signature. The timestamp is formatted to ISO 8061 specifications.

Important!

The timestamp must be in the Coordinated Universal Time (UTC) timezone.

Example

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x-timestamp: 2014-06-02T15:39:31.2729234Z

Psuedocode Example

In this example, assume that the Callback URL is configured as "https://callbacks.yourdomain.com/sinch/callback/result"

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    ApplicationKey = 669E367E-6BBA-48AB-AF15-266871C28135
    ApplicationSecret = BeIukql3pTKJ8RGL5zo0DA==

    Body
        {
            "id":"1234567890",
            "event":"VerificationResultEvent",
            "method": "sms",
            "identity": {
                "type": "number",
                "endpoint": "+11235551234"
            },
            "status": "PENDING",
            "reason": "“Fraud”",
            "reference": "12345",
            "source": "intercept",
            "custom": "string"
        }

    Request-Body-Content-MD5 = Base64 ( MD5 ( [BODY] ) )
        REWF+X220L4/Gw1spXOU7g==

    StringToSign
        POST
        REWF+X220L4/Gw1spXOU7g==
        application/json
        x-timestamp:2014-09-24T10:59:41Z
        /sinch/callback/result

    Signature = Base64 ( HMAC-SHA256 ( Base64-Decode( ApplicationSecret ), UTF8 ( StringToSign ) ) )
        Tg6fMyo8mj9pYfWQ9ssbx3Tc1BNC87IEygAfLbJqZb4=

    HTTP Authorization Header
        Authorization: Application 669E367E-6BBA-48AB-AF15-266871C28135:Tg6fMyo8mj9pYfWQ9ssbx3Tc1BNC87IEygAfLbJqZb4=

Important

The Application Secret value must be base64-decoded from before it's used for signing.

Callback Request Validation

Your development platform that receives the callbacks can verify that the request originated from Sinch by calculating the signature as described above and compare the result with the value contained in the Application HTTP header.

Sample repository

You can clone this repository to see how this is implemented in Java, ASP.NET, Python, PHP, and Node.js.