Flask Integration - Finance District Developer Hub

Coming soon. The prism-flask package is not yet published to PyPI. This page describes the planned API.

Overview

The prism-flask package provides Flask middleware for payment-protecting your API routes using the x402 protocol. It uses Flask’s decorator pattern and request context for seamless integration.

Pythonic API

Flask decorators and context managers

Request Context

Payment info in g.prism_payer

Minimal Setup

Single function call to configure

Installation

pip
Poetry
requirements.txt

pip install prism-flask

bash poetry add prism-flask

prism-flask==1.0.0

The canonical SDK config is identify_token (PRISM_IDENTIFY_TOKEN env var) — formerly api_key / PRISM_API_KEY. SDKs accept the legacy names as fallback during the migration window; new code should use the canonical names.

Quick Start

from flask import Flask, g, jsonify
from prism_flask import prism_payment_middleware
from prism_sdk_core import PrismMiddlewareConfig, RoutePaymentConfig

app = Flask(__name__)

# Configure Prism middleware
prism_payment_middleware(
    app,
    config=PrismMiddlewareConfig(
        identify_token='dev-key-123',
        base_url='https://prism-gw.fd.xyz'
    ),
    routes={
        '/api/premium': RoutePaymentConfig(
            price=0.01,
            description='Premium API access'
        )
    }
)

@app.route('/api/premium')
def premium():
    payer = getattr(g, 'prism_payer', None)
    return jsonify({
        'message': 'Premium content!',
        'payer': payer
    })

if __name__ == '__main__':
    app.run(port=5000)

Configuration

Middleware Configuration

from prism_sdk_core import PrismMiddlewareConfig

config = PrismMiddlewareConfig(
    identify_token='your-project-identify-token',        # Required: Your Prism API key
    base_url='https://...',        # Optional: Gateway URL
    debug=True                     # Optional: Enable debug logging
)

Route Configuration

from prism_sdk_core import RoutePaymentConfig

routes = {
    '/api/premium': RoutePaymentConfig(
        price=0.01,                # Price in USD (0.01 = $0.01)
        description='Premium API'  # Human-readable description
    )
}

Route Protection Patterns

Exact Path Matching

prism_payment_middleware(
    app,
    config=config,
    routes={
        '/api/premium': RoutePaymentConfig(
            price=0.01,
            description='Premium API'
        ),
        '/api/weather': RoutePaymentConfig(
            price='$0.001',
            description='Weather data'
        )
    }
)

# ✅ Protected: GET /api/premium
# ✅ Protected: GET /api/weather
# ❌ Not protected: GET /api/public

Wildcard Matching

prism_payment_middleware(
    app,
    config=config,
    routes={
        '/api/*': RoutePaymentConfig(
            price=0.005,
            description='API access'
        )
    }
)

# ✅ Protected: GET /api/users
# ✅ Protected: GET /api/posts/123
# ❌ Not protected: GET /public

Multiple Route Groups

prism_payment_middleware(
    app,
    config=config,
    routes={
        # Free tier
        '/api/basic/*': RoutePaymentConfig(
            price='$0.0001',
            description='Basic API'
        ),

        # Premium tier
        '/api/premium/*': RoutePaymentConfig(
            price='$0.01',
            description='Premium API'
        ),

        # Specific expensive endpoint
        '/api/ai/generate': RoutePaymentConfig(
            price='$0.50',
            description='AI content generation'
        )
    }
)

Accessing Payment Information

Payment info is stored in Flask’s g context object:

from flask import g

@app.route('/api/premium')
def premium():
    # Access payer wallet address
    payer = getattr(g, 'prism_payer', None)
    # Returns: '0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb' or None

    # Access full payment object
    payment = getattr(g, 'prism_payment', None)
    """
    {
        'scheme': 'eip3009',
        'network': 'eth-sepolia',
        'asset': 'usdc',
        'amount': '10000',
        'recipient': '0x...',
        'nonce': '0x...',
        'validBefore': 1735430400,
        'signature': '0x...'
    }
    """

    return jsonify({
        'message': 'Premium content',
        'payer': payer,
        'network': payment.get('network') if payment else None
    })

Safe Access Helper

def get_payer():
    """Safely get payer address from request context"""
    return getattr(g, 'prism_payer', None)

def get_payment():
    """Safely get full payment object from request context"""
    return getattr(g, 'prism_payment', None)

@app.route('/api/data')
def data():
    payer = get_payer()

    if not payer:
        return jsonify({'error': 'Payment required'}), 402

    return jsonify({
        'data': [1, 2, 3],
        'payer': payer
    })

Settlement Validation

The Flask middleware uses @app.after_request decorator to validate settlement before sending data:

# Internal implementation (automatic!)
@app.after_request
def settlement_validation(response):
    """Validate settlement before sending response"""

    settlement_result = g.get('prism_settlement_result')

    if not settlement_result or not settlement_result.get('success'):
        # ❌ Settlement failed - return error instead of data
        error_reason = (settlement_result or {}).get('errorReason', 'Settlement processing failed')
        return jsonify({
            'x402Version': 2,
            'error': 'Payment settlement failed',
            'details': error_reason
        }), 402

    # ✅ Settlement succeeded - add header and return original response
    response.headers['X-PAYMENT-RESPONSE'] = settlement_result['transaction']
    return response

Key Points:

@app.after_request runs after view function but before sending to client
Can return a different response if settlement fails
Works with all Flask response types (jsonify(), make_response(), etc.)

See Stablecoin Settlement for details.

Error Handling

Payment Errors

When a request lacks valid payment:

HTTP/1.1 402 Payment Required

{
  "x402Version": 2,
  "paymentRequired": true,
  "acceptedPayments": [
    {
      "scheme": "eip3009",
      "network": "eth-sepolia",
      "asset": "usdc",
      "amount": "10000",
      "recipient": "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb",
      "nonce": "0xabc123...",
      "validBefore": 1735430400
    }
  ],
  "description": "Premium API access",
  "priceUSD": "0.01"
}

Gateway Errors

HTTP/1.1 500 Internal Server Error

{
  "x402Version": 2,
  "error": "Gateway Error",
  "details": "Failed to contact payment gateway",
  "gateway": {
    "traceId": "abc-123-xyz",
    "timestamp": "2025-12-18T10:30:00Z"
  }
}

Custom Error Handlers

from werkzeug.exceptions import HTTPException

@app.errorhandler(402)
def handle_payment_required(error):
    """Custom handler for payment required errors"""
    return jsonify({
        'error': 'Payment required',
        'message': 'Please provide payment to access this resource',
        'documentation': 'https://apps.fd.xyz/prism/'
    }), 402

@app.errorhandler(500)
def handle_internal_error(error):
    """Custom handler for internal errors"""
    app.logger.error(f'Internal error: {error}')
    return jsonify({
        'error': 'Internal server error',
        'message': 'Something went wrong'
    }), 500

Testing

Unit Testing with pytest

import pytest
from flask import Flask
from prism_flask import prism_payment_middleware
from prism_sdk_core import PrismMiddlewareConfig, RoutePaymentConfig

@pytest.fixture
def app():
    """Create test Flask app"""
    app = Flask(__name__)

    prism_payment_middleware(
        app,
        config=PrismMiddlewareConfig(
            identify_token='test-key',
            base_url='http://test-gateway'
        ),
        routes={
            '/api/premium': RoutePaymentConfig(
                price=0.01,
                description='Test'
            )
        }
    )

    @app.route('/api/premium')
    def premium():
        from flask import g, jsonify
        payer = getattr(g, 'prism_payer', None)
        return jsonify({'message': 'Premium', 'payer': payer})

    return app

@pytest.fixture
def client(app):
    """Create test client"""
    return app.test_client()

def test_payment_required(client):
    """Test 402 response without payment"""
    response = client.get('/api/premium')

    assert response.status_code == 402
    assert response.json['paymentRequired'] == True

def test_valid_payment(client):
    """Test access with valid payment"""
    # Mock payment header
    payment = {
        'scheme': 'eip3009',
        'network': 'eth-sepolia',
        'asset': 'usdc',
        'amount': '10000',
        'signature': '0x' + '0' * 130
    }

    response = client.get(
        '/api/premium',
        headers={'X-PAYMENT': str(payment)}
    )

    # In test mode, mock signatures are accepted
    assert response.status_code == 200
    assert response.json['message'] == 'Premium'

Integration Testing

import requests
import json

def test_full_payment_flow():
    """Test complete payment flow with real Gateway"""
    base_url = 'http://localhost:5000'

    # 1. Request without payment
    response = requests.get(f'{base_url}/api/premium')
    assert response.status_code == 402

    payment_req = response.json()['acceptedPayments'][0]

    # 2. Sign payment with wallet (use web3.py)
    from eth_account import Account
    from eth_account.messages import encode_structured_data

    private_key = 'your-test-private-key'
    account = Account.from_key(private_key)

    # EIP-712 structured data
    structured_data = {
        'types': {
            'EIP712Domain': [...],
            'TransferAuthorization': [...]
        },
        'domain': {...},
        'message': payment_req
    }

    signed = account.sign_message(encode_structured_data(structured_data))

    payment = {
        **payment_req,
        'signature': signed.signature.hex()
    }

    # 3. Send request with signed payment
    response = requests.get(
        f'{base_url}/api/premium',
        headers={'X-PAYMENT': json.dumps(payment)}
    )

    assert response.status_code == 200
    assert 'X-PAYMENT-RESPONSE' in response.headers  # Transaction hash

Production Deployment

Environment Variables

# .env
PRISM_IDENTIFY_TOKEN=your-production-identify-token
PRISM_BASE_URL=https://prism-gw.fd.xyz
FLASK_ENV=production

Production Configuration

import os
from flask import Flask
from prism_flask import prism_payment_middleware
from prism_sdk_core import PrismMiddlewareConfig, RoutePaymentConfig

app = Flask(__name__)

# Load config from environment
prism_payment_middleware(
    app,
    config=PrismMiddlewareConfig(
        identify_token=os.getenv('PRISM_IDENTIFY_TOKEN'),
        base_url=os.getenv('PRISM_BASE_URL'),
        debug=os.getenv('FLASK_ENV') != 'production'
    ),
    routes={
        '/api/premium': RoutePaymentConfig(
            price=0.01,
            description='Premium API'
        )
    }
)

Logging & Monitoring

import logging
from flask import Flask, g

# Configure logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s'
)
logger = logging.getLogger(__name__)

app = Flask(__name__)

@app.before_request
def log_request():
    """Log incoming requests"""
    logger.info(f'Request: {request.method} {request.path}')

@app.after_request
def log_response(response):
    """Log payment events"""
    if response.status_code == 402:
        logger.info(f'Payment required: {request.path}')
    elif response.status_code == 200 and hasattr(g, 'prism_payer'):
        payer = getattr(g, 'prism_payer')
        tx_hash = response.headers.get('X-PAYMENT-RESPONSE')
        logger.info(f'Payment succeeded: {request.path} | Payer: {payer} | TX: {tx_hash}')

    return response

WSGI Deployment (Gunicorn)

# Install Gunicorn
pip install gunicorn

# Run with multiple workers
gunicorn -w 4 -b 0.0.0.0:5000 app:app

# gunicorn.conf.py
bind = "0.0.0.0:5000"
workers = 4
worker_class = "sync"
timeout = 30
keepalive = 2

# Logging
accesslog = "/var/log/gunicorn/access.log"
errorlog = "/var/log/gunicorn/error.log"
loglevel = "info"

Type Hints

Full type hint support with mypy:

from typing import Optional, Dict, Any
from flask import Flask, g, jsonify, Response
from prism_flask import prism_payment_middleware
from prism_sdk_core import PrismMiddlewareConfig, RoutePaymentConfig

app: Flask = Flask(__name__)

def get_payer() -> Optional[str]:
    """Get payer address from request context"""
    return getattr(g, 'prism_payer', None)

def get_payment() -> Optional[Dict[str, Any]]:
    """Get payment object from request context"""
    return getattr(g, 'prism_payment', None)

@app.route('/api/premium')
def premium() -> Response:
    """Payment-protected endpoint"""
    payer: Optional[str] = get_payer()

    return jsonify({
        'message': 'Premium content',
        'payer': payer
    })

Examples

AI Agent API

from flask import Flask, request, jsonify, g
from prism_flask import prism_payment_middleware
from prism_sdk_core import PrismMiddlewareConfig, RoutePaymentConfig

app = Flask(__name__)

prism_payment_middleware(
    app,
    config=PrismMiddlewareConfig(identify_token='your-project-identify-token'),
    routes={
        '/api/ai/chat': RoutePaymentConfig(
            price='$0.01',
            description='AI chat response'
        ),
        '/api/ai/image': RoutePaymentConfig(
            price='$0.50',
            description='AI image generation'
        )
    }
)

@app.route('/api/ai/chat', methods=['POST'])
def ai_chat():
    """AI chat endpoint"""
    data = request.get_json()
    message = data.get('message')
    payer = getattr(g, 'prism_payer')

    # Call AI service
    response = call_ai_service(message)

    return jsonify({
        'response': response,
        'payer': payer,
        'credits_used': 1
    })

Content Paywall

@app.route('/articles/<int:article_id>')
def get_article(article_id):
    """Payment-protected article access"""
    payer = getattr(g, 'prism_payer')

    article = db.get_article(article_id)

    return jsonify({
        'id': article.id,
        'title': article.title,
        'content': article.content,
        'author': article.author,
        'payer': payer
    })

Premium API with Rate Limiting

from flask_limiter import Limiter
from flask_limiter.util import get_remote_address

limiter = Limiter(
    app=app,
    key_func=get_remote_address,
    default_limits=["100 per hour"]
)

@app.route('/api/premium')
@limiter.limit("10 per minute")  # Additional rate limit for premium
def premium():
    """Rate-limited premium endpoint"""
    payer = getattr(g, 'prism_payer')

    return jsonify({
        'message': 'Premium content',
        'payer': payer
    })

Troubleshooting

ImportError: cannot import name 'prism_payment_middleware'

Make sure you installed the correct package:

pip install prism-flask  # Not prism-sdk-core alone

Check Python version:

python --version  # Requires Python 3.8+

g.prism_payer is None even with valid payment

Check: 1. Payment header is properly formatted JSON string 2. Middleware is configured BEFORE route definitions 3. Route path matches configured route pattern 4. Payment signature is valid Debug:

python @app.before_request       def debug_payment(): print(f'Path: {request.path}') print(f'Payment header:{" "}   {request.headers.get("X-PAYMENT")}') print(f'Payer:{" "}   {getattr(g, "prism_payer", "NOT SET")}')

Settlement fails but payment was valid

Common causes: 1. Insufficient balance in sender’s wallet 2. Token allowance not set for USDC contract 3. Network congestion (transaction timeout) 4. Nonce already used (replay attack prevention) Check logs: python import logging logging.basicConfig(level=logging.DEBUG)

Type hints not working in IDE

Install type stubs:

pip install types-Flask

Configure mypy:

# mypy.ini
[mypy]
python_version = 3.8
plugins = sqlmypy

Flask-CORS Integration

Enable CORS for browser-based clients:

from flask import Flask
from flask_cors import CORS
from prism_flask import prism_payment_middleware

app = Flask(__name__)

# Configure CORS
CORS(app, resources={
    r"/api/*": {
        "origins": ["https://yourapp.com"],
        "methods": ["GET", "POST"],
        "allow_headers": ["Content-Type", "X-PAYMENT"],
        "expose_headers": ["X-PAYMENT-RESPONSE"]
    }
})

# Then configure Prism
prism_payment_middleware(app, config, routes)

Blueprint Support

Works with Flask Blueprints:

from flask import Blueprint, g, jsonify

api_bp = Blueprint('api', __name__, url_prefix='/api')

@api_bp.route('/premium')
def premium():
    """Blueprint route - payment still works!"""
    payer = getattr(g, 'prism_payer')
    return jsonify({'message': 'Premium', 'payer': payer})

# Register blueprint
app.register_blueprint(api_bp)

# Configure Prism with blueprint routes
prism_payment_middleware(
    app,
    config=config,
    routes={
        '/api/premium': RoutePaymentConfig(price=0.01, description='Premium')
    }
)

​Overview

Pythonic API

Request Context

Minimal Setup

​Installation

​Quick Start

​Configuration

​Middleware Configuration

​Route Configuration

​Route Protection Patterns

​Exact Path Matching

​Wildcard Matching

​Multiple Route Groups

​Accessing Payment Information

​Safe Access Helper

​Settlement Validation

​Error Handling

​Payment Errors

​Gateway Errors

​Custom Error Handlers

​Testing

​Unit Testing with pytest

​Integration Testing

​Production Deployment

​Environment Variables

​Production Configuration

​Logging & Monitoring

​WSGI Deployment (Gunicorn)

​Type Hints

​Examples

​AI Agent API

​Content Paywall

​Premium API with Rate Limiting

​Troubleshooting

​Flask-CORS Integration

​Blueprint Support

Overview

Installation

Quick Start

Configuration

Middleware Configuration

Route Configuration

Route Protection Patterns

Exact Path Matching

Wildcard Matching

Multiple Route Groups

Accessing Payment Information

Safe Access Helper

Settlement Validation

Error Handling

Payment Errors

Gateway Errors

Custom Error Handlers

Testing

Unit Testing with pytest

Integration Testing

Production Deployment

Environment Variables

Production Configuration

Logging & Monitoring

WSGI Deployment (Gunicorn)

Type Hints

Examples

AI Agent API

Content Paywall

Premium API with Rate Limiting

Troubleshooting

Flask-CORS Integration

Blueprint Support