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SpankPay APIs

Purchase

A purchase is a request for a payment. When created with the Button API or the JavaScript API, the user will be presented with a payment form prompting them to send cryptocurrency equivalent in value to the requested amount. Once the cryptocurrency has been received, the callback webhook will be called, and the Button/JavaScript onPurchaseComplete callback called.

Input Currencies

The Input Currency for a Purchase is the currency used by the user to pay for the purchase.

Currently valid input currencies:

Output Currencies

The Output Currency for a Purchase is the currency which will be displayed to the user, and the currency which will be credited to your account. For example, a US$10 Purchase will have "amount": "10.00" and "currency": "USD". When paying, the user will be given the option to pay with (for example) 0.074 ETH or 0.0026 BTC.

Currently valid output currencies:

Creating a Purchase with a Button

A SpankPay button is the simplest way to accept SpankPay on your site.

When the button is clicked, the user will be presented with the SpankPay purchase frame, and the data-on-payment callback will be called once the payment is complete and your callback has accepted the payment.

<script src="https://pay.spankchain.com/spankpay.js"></script>

<script>
function onSpankPayPayment(payment) {
  console.log(`Payment ${payment.status}`, payment)
}
</script>

<button
    data-spankpay-key="test_quickstart_key"
    data-amount="69.69"
    data-currency="USD"
    data-accept-currencies="BOOTY,ETH,BTC,DOGE"
    data-metadata="{&quot;orderId&quot;: &quot;sc696969&quot;}"
    data-callback="https://pay.spankchain.com/api/quickstart/callback"
    data-on-payment="onSpankPayPayment">
  Pay with SpankPay!
</button>

See also:

Creating a Purchase with the SpankPay JavaScript API

For complete control over the user's SpankPay experience, the API can be called directly.

The SpankPay.showPurchase(...) method can be used to show the SpankPay purchase frame.

const { SpankPay } = require('spankpay')

const frame = SpankPay.showPurchase({
  key: 'test_quickstart_key',
  amount: '69.69',
  currency: 'USD',
  acceptCurrencies: ['BOOTY', 'ETH', 'BTC', 'DOGE'],
  metadata: {
    orderId: 'sc696969',
  },
  callback: 'https://pay.spankchain.com/api/quickstart/callback',
})

frame.on('payment', payment => {
  console.log(`Payment ${payment.status}`, payment)
})

frame.on('stateChange', state => {
  console.log('Frame state:', state)
})

frame.on('close', () => {
  console.log('Frame was closed!')
})

See also:

Purchase Frame Events

Events can be handled either by passing a callback to SpankPay.showPurchase(...), or binding to the event on the returned frame object:

const frame = SpankPay.showPurchase({
  onStateChange: state => { ... },
})
frame.on('payment', payment => { ... })

Frame State

The purchase frame state, exposed through frame.state and the stateChange event, has the following fields:

payment Event

The payment event will be triggered when a payment has been received and the callback url has accepted the payment.

The payment argument will be a Payment object, and the status should be checked to ensure the payment has succeeded. Note, however, that the payment will only fail if the callback rejects the payment (see: Webhook Expected Response).

For example:

function onPayment(payment) {
  console.log(`Payment ${payment.status}:`, payment)
  if (payment.status == "succeeded") {
    window.location.href = '/order-complete'
  } else {
    window.location.href = '/order-failed'
  }
}

Payment

A payment is created when SpankPay receives a user's payment in response to a Purchase.

The callback URL is provided when the Purchase is created, and we recommend including some metadata in the URL which your application can use to credit the appropriate order.

For example, if you assign each order an ID, the callback URL might be https://your-site.com/api/spankpay/callback?order-id=sc696969.

Webhook Format

Webhook messages will take the following format:

POST /api/quickstart/callback
Content-Type: text/plain
X-SpankPay-Key: test_quickstart_key
X-SpankPay-Signature: t=1551389518&s=b613679a0814d9ec…

{
    "type": "payment",
    "payment_id": "pay_c493715653c",
    "timestamp": "1969-06-09T06:09:06.969Z",
    "purchaseId": "pur_f95d778c35f",
    "purchase": { ... },
    "amount": "69.69",
    "amountCurrency": "USD",
    "inputAmount": "0.6969",
    "inputCurrency": "ETH",
    "inputTx": "0x2144292c5ad…",
    "receipt": {
        "type": "webhook",
        "url": "https://yoursite.com/yourserver/callback",
        "status": "called",
        "calledOn": "1969-06-09T06:09:06.969Z",
        "responseStatusCode": 200,
        "response": ...,
        ...
    }
    ...
}

The type field will always be "payment", although there may be other types in the future. The rest of the body will be a Payment object.

Note: the Content-Type will be text/plain instead of application/json as might be expected. This is to ensure that web frameworks like Express do not attempt to parse the request body as JSON, and instead make the raw string available to the request handler so it can more easy check the signature.

Expected Response

The webhook endpoint must return an HTTP 200 response with a JSON object containing { "received": true }. Other metadata may optionally be included in the JSON object, and it will be returned verbatim in the Payment's receipt.response field.

A payment will be considered failed if the response contains either { "received": false }, or an HTTP status code of 4XX. On a failed payment, the user will be refunded their cryptocurrency (less standard transaction fees) and the payment will be marked "failed".

If the webhook endpoint returns a non-200 response, or a body that does not contain { "received": true }, the webhook will be retried according to the following rules:

  • 10 times, each 30 seconds apart (ie, every 30 seconds for 5 minutes)

  • 10 times, each 5 minutes apart (ie, every 5 minutes for 50 minutes)

  • 10 times, each 60 minutes apart (ie, every 1 hour for 10 hours)

If all retries fail, the API key administrator will be notified. A webhook can be manually retried at any point through the administrative UI.

Testing Webhooks

The Webhook Test Page (not yet available) can be used to send simulated webhooks.

(this will be a page with inputs for URL, public key, secret key, various payment fields, and a button which - when clicked - will trigger a webhook call to the provided URL).

Note: the webhook test page can only be used with testing keys (ie, keys prefixed with "test_"), and all currencies will be "TEST-" currencies.

Additionally, we recommend that developers use ngrok to create a public URL which can route to their local development server. During development, your application can be configured to automatically query ngrok for the developer's current public URL:

async function getPublicUrl() {
  if (config.PUBLIC_URL)
    return config.PUBLIC_URL

  if (!config.ENVIRONMENT != 'development')
    throw new Error('config.PUBLIC_URL has not been defined!')

  try {
    const res = await fetch('http://localhost:4040/api/tunnels')
  } catch (e) {
    throw new Error(
      'Error connecting to ngrok to fetch public URL ' +
      '(hint: did you run "ngrok"?). Original error: ' + e
    )
  }

  const obj = await res.json()
  for (const tun of obj.tunnels) {
    return tun.public_url
  }

  throw new Error(
    'Unexpected response from ngrok (tunnels found): ' +
    JSON.stringify(obj)
  )
}

Security

To verify that webhooks are authentically from SpankPay, the content can be verified using the X-SpankPay-Signature header.

We strongly recommend validating webhook signatures, otherwise it could be possible for an attacker to create fake payment confirmations.

Validating Webhook Signatures

const { SpankPay } = require('spankpay')

app.post('/spankpay/callback', (req, res) => {
    const key = req.headers['x-spankpay-key']
    if (key != process.env.SPANKPAY_API_KEY) {
        console.error(
            `Unexpected SpankPay API key: ` +
            `${key} != ${process.env.SPANKPAY_API_KEY}`
        )
        return res.status(400)
    }

    const [data, timestamp, err] = SpankPay.decodeWebhook(
        req.body,
        req.headers['x-spankpay-signature'],
        process.env.SPANKPAY_API_SECRET,
    )
    if (err) {
        console.error('Error decoding SpankPay webhook:', err)
        return res.status(400)
    }

    const age = (Date.now() / 1000) - timestamp
    if (age > 60 * 10) {
        console.error(`SpankPay webhook too old (was created ${age}s ago)`)
        return res.status(400)
    }

    // ... handle webhook ...

    return res.json({ received: true })
})

Preventing Replay Attacks

To ensure your application only processes each webhook once, we recommend using the signature as a nonce. For example:

app.post('/spankpay/callback', async (req, res) => {
    const sig = req.headers['x-spankpay-signature']
    // ... validate signature ...

    try {
        const firstUse = await redis.set(`spankpay-webhook:${sig}`, '1', {
            // The nx - Not Exists - flag ensures the key can only be set once
            nx: true,
            // The ex - EXpire - flag ensures the key will expire after an hour
            ex: 60 * 60,
        })
        if (!firstUse)
            return res.json({ received: true })

        // ... handle webhook ...
    } catch (e) {
        // If there is an error, clear the flag so that the webhook
        // will be processed on a subsequent request.
        // NOTE: your application must be careful not to leave the
        //       webhook in a partially processed state, otherwise
        //       there may be inconsistencies when it is retried.
        await redis.del(`spankpay-webhook:${sig}`)
        throw e
    }

    return res.json({ received: true })
})
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