Open Banking Integration (PSD2)
Open Banking requires banks to provide third parties with access to customer account data and payment initiation capabilities through standardized APIs.
Account Information Service (AIS)
AIS providers access customer account data with explicit consent:
// Step 1: Request consent
POST /oauth/authorize
{
"client_id": "aisp_client_123",
"redirect_uri": "https://fintech.example.com/callback",
"scope": "accounts transactions",
"permissions": [
"ReadAccountsBasic",
"ReadAccountsDetail",
"ReadTransactionsBasic",
"ReadTransactionsDetail"
],
"expiration_date": "2026-12-25T23:59:59Z"
}
// Step 2: Retrieve accounts
GET /open-banking/v3.1/aisp/accounts
Authorization: Bearer {access_token}
Response:
{
"Data": {
"Account": [
{
"AccountId": "ACC-12345",
"Currency": "GBP",
"AccountType": "Personal",
"AccountSubType": "CurrentAccount",
"Nickname": "Main Account"
}
]
}
}
// Step 3: Get transactions
GET /open-banking/v3.1/aisp/accounts/ACC-12345/transactions
Authorization: Bearer {access_token}
Response:
{
"Data": {
"Transaction": [
{
"TransactionId": "TXN-001",
"Amount": {
"Amount": "150.00",
"Currency": "GBP"
},
"CreditDebitIndicator": "Debit",
"Status": "Booked",
"BookingDateTime": "2025-12-24T14:30:00Z",
"MerchantDetails": {
"MerchantName": "Coffee Shop Ltd"
}
}
]
}
}
Payment Initiation Service (PIS)
PIS providers can initiate payments on behalf of customers:
// Initiate single domestic payment
POST /open-banking/v3.1/pisp/domestic-payments
Authorization: Bearer {access_token}
x-idempotency-key: {unique-key}
{
"Data": {
"Initiation": {
"InstructionIdentification": "PMT-2025-001",
"EndToEndIdentification": "E2E-12345",
"InstructedAmount": {
"Amount": "500.00",
"Currency": "GBP"
},
"DebtorAccount": {
"SchemeName": "UK.OBIE.SortCodeAccountNumber",
"Identification": "40400411290112",
"Name": "John Smith"
},
"CreditorAccount": {
"SchemeName": "UK.OBIE.SortCodeAccountNumber",
"Identification": "08080021325698",
"Name": "ACME Corp"
},
"RemittanceInformation": {
"Unstructured": "Invoice 12345"
}
}
}
}
Payment Gateway Integration
Payment gateways process card payments, digital wallets, and alternative payment methods.
Card Payment Flow
// Create payment intent
POST /v1/payment-intents
{
"amount": 2500,
"currency": "usd",
"payment_method_types": ["card"],
"metadata": {
"order_id": "ORDER-12345"
}
}
Response:
{
"id": "pi_abc123",
"client_secret": "pi_abc123_secret_xyz",
"status": "requires_payment_method",
"amount": 2500,
"currency": "usd"
}
// Client confirms payment (with 3D Secure)
POST /v1/payment-intents/pi_abc123/confirm
{
"payment_method": "pm_card_visa",
"return_url": "https://shop.example.com/complete"
}
// Webhook notification
POST https://shop.example.com/webhook
{
"type": "payment_intent.succeeded",
"data": {
"object": {
"id": "pi_abc123",
"status": "succeeded",
"amount_received": 2500,
"charges": {
"data": [
{
"id": "ch_abc123",
"payment_method_details": {
"card": {
"brand": "visa",
"last4": "4242"
}
}
}
]
}
}
}
}
Market Data Distribution
Financial market data must be distributed with extremely low latency to traders and algorithmic trading systems.
WebSocket Market Data Feed
// Subscribe to market data
{
"action": "subscribe",
"symbols": ["AAPL", "GOOGL", "MSFT"],
"channels": ["trades", "quotes", "orderbook"]
}
// Receive trade updates
{
"type": "trade",
"symbol": "AAPL",
"trade_id": "TR-123456",
"price": 150.25,
"size": 100,
"timestamp": 1735138200123,
"conditions": []
}
// Receive quote updates (Level 1)
{
"type": "quote",
"symbol": "AAPL",
"bid": 150.24,
"bid_size": 500,
"ask": 150.26,
"ask_size": 300,
"timestamp": 1735138200456
}
// Receive order book update (Level 2)
{
"type": "orderbook",
"symbol": "AAPL",
"bids": [
[150.24, 500],
[150.23, 1200],
[150.22, 800]
],
"asks": [
[150.26, 300],
[150.27, 900],
[150.28, 600]
],
"timestamp": 1735138200789
}
FIX Protocol for Order Management
// New Order Single (Type D)
8=FIX.4.4|9=200|35=D|49=BROKER|56=EXCHANGE|34=1|52=20251225-14:30:00|
11=ORD-2025-001|21=1|55=AAPL|54=1|60=20251225-14:30:00|38=100|40=2|
44=150.25|59=0|10=123|
Fields explained:
11 = Client Order ID
21 = 1 (Automated execution)
55 = Symbol (AAPL)
54 = 1 (Buy side)
38 = Order quantity (100 shares)
40 = 2 (Limit order)
44 = Price (150.25)
59 = 0 (Day order)
// Execution Report (Type 8)
8=FIX.4.4|9=250|35=8|49=EXCHANGE|56=BROKER|34=2|52=20251225-14:30:01|
37=EXCH-ORD-123|11=ORD-2025-001|17=FILL-001|150=2|39=2|55=AAPL|54=1|
38=100|44=150.25|32=100|31=150.25|151=0|14=100|6=150.25|10=234|
Fields explained:
150 = 2 (Fill)
39 = 2 (Filled)
32 = Last filled quantity (100)
31 = Last filled price (150.25)
151 = Remaining quantity (0)
14 = Cumulative quantity (100)
6 = Average price (150.25)
Core Banking System Integration
Integrating with legacy core banking systems requires careful handling of mainframe protocols and batch processing.
Real-time Integration Pattern
- API Wrapper: RESTful API layer over core banking
- Message Queue: Decouple request/response timing
- Data Cache: Cache frequently accessed data
- Circuit Breaker: Handle core system unavailability
Batch Processing Pattern
// End-of-day batch processing
1. Extract transactions from core system (6:00 PM)
- Query DB2 database
- Generate flat file export
- Transfer via SFTP
2. Transform data (6:30 PM)
- Parse fixed-width format
- Validate data integrity
- Enrich with reference data
3. Load to data warehouse (7:00 PM)
- Bulk insert into PostgreSQL
- Update aggregated tables
- Refresh materialized views
4. Generate reports (8:00 PM)
- Daily transaction summary
- Balance reconciliation
- Exception reports
- Regulatory filings
5. Distribute reports (9:00 PM)
- Email to stakeholders
- Upload to secure portal
- Archive in document management
Regulatory Reporting Automation
Automated regulatory reporting reduces manual effort and improves accuracy.
EMIR Trade Reporting
// Collect trade data
const trades = await db.query(`
SELECT * FROM derivatives_trades
WHERE trade_date = CURRENT_DATE
AND reportable = true
`);
// Transform to EMIR format (ISO 20022)
const emirReport = trades.map(trade => ({
reportingCounterparty: {
id: trade.counterparty_lei,
country: 'GB'
},
otherCounterparty: {
id: trade.client_lei,
country: trade.client_country
},
commonData: {
contractType: trade.product_type,
notionalAmount: trade.notional,
notionalCurrency: trade.currency,
deliveryType: trade.settlement_type
},
underlyingData: {
underlyingId: trade.underlying_isin,
underlyingName: trade.underlying_name
}
}));
// Submit to trade repository
await tradeRepository.submit({
format: 'ISO20022',
data: emirReport,
reportingEntity: 'LEI-1234567890ABCDEFGH',
submissionDate: new Date().toISOString()
});
MiFID II Transaction Reporting
- Report all transactions in financial instruments within 1 working day
- Include 65 data fields per transaction
- Submit to national competent authority (e.g., FCA, AMF)
- Maintain audit trail for 5 years
Event-Driven Integration
Event-driven architectures enable real-time processing and loose coupling between systems.
Event Sourcing Pattern
// Define domain events
interface AccountEvent {
eventId: string;
accountId: string;
timestamp: string;
type: string;
data: unknown;
}
// Events examples
{
"eventId": "EVT-001",
"accountId": "ACC-12345",
"timestamp": "2025-12-25T14:30:00Z",
"type": "ACCOUNT_CREDITED",
"data": {
"amount": 500.00,
"currency": "USD",
"source": "SALARY_PAYMENT"
}
}
{
"eventId": "EVT-002",
"accountId": "ACC-12345",
"timestamp": "2025-12-25T15:45:00Z",
"type": "ACCOUNT_DEBITED",
"data": {
"amount": 150.00,
"currency": "USD",
"recipient": "MERCHANT_ABC"
}
}
// Rebuild account state from events
function rebuildAccountState(events: AccountEvent[]): Account {
return events.reduce((account, event) => {
switch (event.type) {
case 'ACCOUNT_CREATED':
return { ...event.data, balance: 0 };
case 'ACCOUNT_CREDITED':
return { ...account, balance: account.balance + event.data.amount };
case 'ACCOUNT_DEBITED':
return { ...account, balance: account.balance - event.data.amount };
default:
return account;
}
}, {} as Account);
}
These integration patterns form the foundation of modern financial systems. Choosing the right pattern for each use case is essential for building scalable, maintainable solutions.