SNAP BI Payment Gateway Architecture with Go Clean Architecture

1. Overview & What is the SNAP BI Standard?

In accordance with Bank Indonesia's SNAP BI (Standar Nasional Open API Pembayaran) regulation, financial institutions and payment gateways must standardize their B2B integration protocols. This case study details the engineering architecture for an enterprise-grade payment gateway engine written in Go (Golang) adhering strictly to Clean Architecture principles.

The primary engineering challenge in building a compliant payment gateway is handling high-velocity cryptographic verifications and state transitions without increasing P99 latency, all while guaranteeing absolute ACID transaction consistency.

2. End-to-End Sequence & Transaction Flow

3. Cryptographic Signature Verification in Go

The SNAP BI standard mandates validating normalized payload strings (constructed from HTTPMethod + ":" + EndpointPath + ":" + AccessToken + ":" + MinifiedBodyHash + ":" + Timestamp). Below is a clean implementation of the symmetric signature generator constructed in the Delivery / Middleware Layer:

package snapbi

import (
	"crypto/hmac"
	"crypto/sha512"
	"encoding/hex"
	"fmt"
	"strings"
)

// GenerateSymmetricSignature calculates the SNAP BI compliant X-SIGNATURE
func GenerateSymmetricSignature(httpMethod, endpointPath, accessToken, minifiedBody, timestamp, clientSecret string) string {
	// 1. Calculate lowercase hex SHA256 hash of minified JSON body
	hasher := sha512.New256()
	hasher.Write([]byte(minifiedBody))
	bodyHash := strings.ToLower(hex.EncodeToString(hasher.Sum(nil)))

	// 2. Build string-to-sign according to Bank Indonesia specification
	stringToSign := fmt.Sprintf("%s:%s:%s:%s:%s",
		strings.ToUpper(httpMethod),
		endpointPath,
		accessToken,
		bodyHash,
		timestamp,
	)

	// 3. Compute HMAC-SHA512 using Merchant Client Secret
	mac := hmac.New(sha512.New, []byte(clientSecret))
	mac.Write([]byte(stringToSign))
	return hex.EncodeToString(mac.Sum(nil))
}

4. Preventing Double-Debits with Distributed Idempotency Locks

Under mobile network instability or gateway timeouts, merchants often retry unacknowledged payment requests. To guarantee that a transaction is executed exactly once:

5. High-Throughput Double-Entry Ledger & Consistency

By architecting the platform around Go Clean Architecture and PostgreSQL partitioned tables, domain entities remain decoupled from transport protocols. The service easily sustains thousands of requests per second (TPS) with sub-50ms P99 latency while adhering to Bank Indonesia regulatory standards.