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POST /v1/proxy/webhook-relay 2 tokens API key Proxy

Secure Webhook Relay Proxy with HMAC SHA-256 signature generation

Secure Webhook Relay Proxy with HMAC SHA-256 signature generation, automated exponential backoff retries, and attempt metrics

POST

Request

  • x-api-key: <your-api-key>
  • Content-Type: application/json

Response 

{
  "attemptsLog": [
    {
      "attempt": 36,
      "error": "<error>",
      "latencyMs": 17,
      "statusCode": 200,
      "success": true
    }
  ],
  "delivered": true,
  "finalStatusCode": 200,
  "responseBody": {},
  "signatureAttached": true,
  "signatureHeaderName": "Ada Lovelace",
  "status": "success",
  "targetUrl": "https://example.com/page",
  "tokensDeducted": 2,
  "totalAttempts": 3,
  "totalExecutionTimeMs": 3
}
The response below is a mock built from the endpoint's own schema — no request leaves this page. Edit the body, press Send, read the shape you will get back. Run it for real in the dashboard →

What it does

Secure Webhook Relay Proxy with HMAC SHA-256 signature generation, automated exponential backoff retries, and attempt metrics

Request

Body

FieldTypeRequiredDescription
customHeadersobjectno
maxRetriesintegernoMaximum retry attempts for 5xx errors or connection timeouts
payloadobject | array | stringyesJSON object/array or raw string payload to deliver
secretstringnoOptional secret key used to generate HMAC SHA-256 signature
signatureEncodingenumnoOne of: hex, base64.
signatureHeaderstringnoHeader name under which the generated HMAC signature is attached
targetUrlstringyes
timeoutintegernoTimeout per HTTP request attempt in ms

Example request

{
  "customHeaders": {},
  "maxRetries": 3,
  "payload": {},
  "secret": "<secret>",
  "signatureEncoding": "hex",
  "signatureHeader": "X-Signature-SHA256",
  "targetUrl": "https://example.com/page",
  "timeout": 5000
}

Response

FieldTypeDescription
attemptsLogarray<object>
  ↳ attemptinteger
  ↳ errorstring
  ↳ latencyMsinteger
  ↳ statusCodeinteger
  ↳ successboolean
deliveredboolean
finalStatusCodeinteger
responseBodyobject | array | string
signatureAttachedboolean
signatureHeaderNamestring
statusstring
targetUrlstring
tokensDeductedinteger
totalAttemptsinteger
totalExecutionTimeMsinteger

Example response

{
  "attemptsLog": [
    {
      "attempt": 36,
      "error": "<error>",
      "latencyMs": 17,
      "statusCode": 200,
      "success": true
    }
  ],
  "delivered": true,
  "finalStatusCode": 200,
  "responseBody": {},
  "signatureAttached": true,
  "signatureHeaderName": "Ada Lovelace",
  "status": "success",
  "targetUrl": "https://example.com/page",
  "tokensDeducted": 2,
  "totalAttempts": 3,
  "totalExecutionTimeMs": 3
}

Errors

Every error answers with the same envelope: an HTTP status, a machine code and a sentence.

400The body or a parameter failed validation. The details array names the field.
401No key, a revoked key or a wrong header. Send x-api-key.
402The wallet cannot cover this call. Top up or wait for the monthly grant.
404The resource does not exist, or it is not yours. Both answer identically and cost nothing.
429Over the per-minute quota of your tier. Back off and retry.
5xxUpstream refused or timed out. The call is not billed.

Code

curl -X POST 'https://app.castomapi.com/v1/proxy/webhook-relay' \
  -H 'x-api-key: <your-api-key>' \
  -H 'Content-Type: application/json' \
  -d '{"customHeaders": {}, "maxRetries": 3, "payload": {}, "secret": "<secret>", "signatureEncoding": "hex", "signatureHeader": "X-Signature-SHA256", "targetUrl": "https://example.com/page", "timeout": 5000}'
const res = await fetch('https://app.castomapi.com/v1/proxy/webhook-relay', {
  method: 'POST',
  headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
  body: JSON.stringify({"customHeaders": {}, "maxRetries": 3, "payload": {}, "secret": "<secret>", "signatureEncoding": "hex", "signatureHeader": "X-Signature-SHA256", "targetUrl": "https://example.com/page", "timeout": 5000})
});
const data = await res.json();
console.log(data);
import { request } from 'node:https';

// Node 18+ has fetch built in
const res = await fetch('https://app.castomapi.com/v1/proxy/webhook-relay', {
  method: 'POST',
  headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
  body: JSON.stringify({"customHeaders": {}, "maxRetries": 3, "payload": {}, "secret": "<secret>", "signatureEncoding": "hex", "signatureHeader": "X-Signature-SHA256", "targetUrl": "https://example.com/page", "timeout": 5000})
});
const data = await res.json();
console.log(data);
import requests

res = requests.post(
    'https://app.castomapi.com/v1/proxy/webhook-relay',
    headers={'x-api-key': '<your-api-key>'},
    json={"customHeaders": {}, "maxRetries": 3, "payload": {}, "secret": "<secret>", "signatureEncoding": "hex", "signatureHeader": "X-Signature-SHA256", "targetUrl": "https://example.com/page", "timeout": 5000},
    timeout=30,
)
print(res.json())
<?php
$ch = curl_init('https://app.castomapi.com/v1/proxy/webhook-relay');
curl_setopt_array($ch, [
    CURLOPT_CUSTOMREQUEST => 'POST',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
    CURLOPT_POSTFIELDS => json_encode(['customHeaders' => [], 'maxRetries' => 3, 'payload' => [], 'secret' => '<secret>', 'signatureEncoding' => 'hex', 'signatureHeader' => 'X-Signature-SHA256', 'targetUrl' => 'https://example.com/page', 'timeout' => 5000]),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);

Cost and limits

This operation costs 2 tokens. A call that fails is never billed. Every account gets 1000 free tokens a month; paid balances never expire.

Rate limits per minute

No key10
Free60
Pro300
Enterprise1200

Docs → Pricing

Questions

What does Secure Webhook Relay Proxy with HMAC SHA-256 signature generation cost?

2 tokens per successful call, debited from your wallet after the response. Failed calls are free. Every account receives 1000 free tokens a month.

How do I authenticate?

Send your key in the x-api-key header. One key covers every metered endpoint; there is nothing to enable per endpoint.

Can I send an Authorization: Bearer token instead?

Not for a metered endpoint — those take the x-api-key header and nothing else. Bearer tokens belong to the account side: the dashboard and account APIs accept a JWT session, and castomapi-auth issues those through a standard OAuth2 handshake, with authorization code, client credentials and refresh grants. The auth service page covers it.

What are the limits?

10 requests a minute per IP with no key at all, 60 a minute on the free tier, 300 on Pro, 1200 on Enterprise. Above the no-key tier the quota is per account, across every endpoint.

OpenAPI: https://app.castomapi.com/docs/json