Generate X-Custom-Signature - Waftpay Developer Docs

Some Waftpay APIs, notably Payouts and Remittance, require a request header called X-Custom-Signature. This signature lets our platform verify who sent the request and that its key fields were not altered in transit.

TL;DR

Get a Bearer token (Auth token).

Generate an RSA 2048 key pair; register your public key with Waftpay.

Build the signing string: transaction.reference + transaction.amount + originator.country + transaction.service_code with no separators.

Sign with RSA + SHA-256, Base64-encode the signature bytes, and send it in X-Custom-Signature.

When it’s required

Payouts: POST /payments/v1/payouts
Remittance: POST /payments/v1/remittance

These endpoints also require Bearer auth in the Authorization header.

Environments

Environment	Base URL
Sandbox	`https://dev.waftpay.io`
Production	`https://api.waftpay.io`

Use separate key pairs for Sandbox and Production. Register the correct public key for each environment.

Prerequisites

Valid Bearer token in Authorization: Bearer <access_token> (see Auth token).
RSA 2048 key pair in PEM; public key registered with Waftpay.
Make sure the values you sign exactly match the payload you send, including casing and formatting.

Key handling and security

Never commit private keys to your repo or docs site. Treat them as secrets.
Store private keys in a secure vault or encrypted filesystem and load them at runtime.
Rotate keys periodically and re-register the public key with Waftpay.
Use different key pairs for Sandbox and Production.

1) Create your key pair (RSA 2048)

You need an RSA 2048 key pair in PEM format:

Private key: PKCS#8 PEM (-----BEGIN PRIVATE KEY-----)
Public key: X.509 SubjectPublicKeyInfo PEM (-----BEGIN PUBLIC KEY-----)

2) Build the signing string

Concatenate these fields in order with no separators:

transaction.reference + transaction.amount + originator.country + transaction.service_code

Use the exact strings you send in the JSON, for example amount "100.00" and country "KE" vs "KEN".
Do not trim, pad, round, or change case once you build the payload.

Example signing string

TXN123654573100.00KENewqeqw

Generate `X-Custom-Signature`

Keep your private key outside the repo, for example ./keys/client_private.pem, and load it at runtime.

Node.js
Python
Java
PHP

import crypto from "crypto";
import fs from "fs";

const txRef = "TXN123654573";
const amount = "100.00"; // stringify exactly as sent
const country = "KEN";   // match payload exactly
const service = "ewqeqw";

const signingString = `${txRef}${amount}${country}${service}`;
const privateKeyPem = fs.readFileSync("client_private.pem", "utf8");

const sig = crypto.sign(
  "RSA-SHA256",
  Buffer.from(signingString, "utf8"),
  privateKeyPem
);

console.log(sig.toString("base64")); // -> X-Custom-Signature

import base64
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import padding

tx_ref = "TXN123654573"
amount = "100.00"
country = "KEN"
service = "ewqeqw"

signing_string = f"{tx_ref}{amount}{country}{service}".encode("utf-8")

with open("client_private.pem", "rb") as f:
    key = serialization.load_pem_private_key(f.read(), password=None)

sig = key.sign(signing_string, padding.PKCS1v15(), hashes.SHA256())

print(base64.b64encode(sig).decode("utf-8"))  # -> X-Custom-Signature

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.Signature;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Base64;

public final class WaftpaySignature {

    public static String generateXCustomSignature(
        String txRef,
        String amount,
        String country,
        String service,
        PrivateKey privateKey
    ) throws Exception {

        String signingString = txRef + amount + country + service;
        byte[] message = signingString.getBytes(StandardCharsets.UTF_8);

        Signature sig = Signature.getInstance("SHA256withRSA");
        sig.initSign(privateKey);
        sig.update(message);

        byte[] raw = sig.sign();

        return Base64.getEncoder().encodeToString(raw);
    }

    public static PrivateKey loadPkcs8PrivateKey(Path pemPath) throws Exception {
        String pem = Files.readString(pemPath, StandardCharsets.US_ASCII);

        String base64 = pem
            .replace("-----BEGIN PRIVATE KEY-----", "")
            .replace("-----END PRIVATE KEY-----", "")
            .replaceAll("\\s", "");

        byte[] der = Base64.getDecoder().decode(base64);
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(der);

        return KeyFactory.getInstance("RSA").generatePrivate(keySpec);
    }

    public static void main(String[] args) throws Exception {
        PrivateKey key = loadPkcs8PrivateKey(Path.of("client_private.pem"));

        String txRef = "TXN123654573";
        String amount = "100.00";
        String country = "KEN";
        String service = "ewqeqw";

        String xCustomSignature = generateXCustomSignature(
            txRef,
            amount,
            country,
            service,
            key
        );

        System.out.println("X-Custom-Signature: " + xCustomSignature);
    }
}

<?php

$txRef = "TXN123654573";
$amount = "100.00";
$country = "KEN";
$service = "ewqeqw";

$signingString = $txRef . $amount . $country . $service;

$privateKey = openssl_pkey_get_private(
    file_get_contents("client_private.pem")
);

openssl_sign($signingString, $rawSig, $privateKey, OPENSSL_ALGO_SHA256);

echo base64_encode($rawSig), PHP_EOL; // -> X-Custom-Signature

Use standard Base64, not Base64URL. The signing algorithm is RSA PKCS#1 v1.5 + SHA-256.

Example request headers

Authorization: Bearer <access_token>
X-Custom-Signature: <base64_signature>
Content-Type: application/json

Common mistakes

Mismatched amount formatting: if you send "100.00" you must sign "100.00", not "100".
Country/service casing: KE vs KEN or service code casing must match exactly.
Wrong key format: use PKCS#8 (BEGIN PRIVATE KEY), not PKCS#1 (BEGIN RSA PRIVATE KEY).
Base64URL vs Base64: use standard Base64 with + and /, not URL-safe Base64.
Payload mismatch: any difference between the signed string and the sent JSON will fail verification.

OpenSSL (Linux/macOS/Windows with OpenSSL)

# 1) Generate a 2048-bit RSA private key (PKCS#8)
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out client_private.pem

# 2) Derive the matching public key (X.509 SPKI)
openssl rsa -pubout -in client_private.pem -out client_public.pem