Library to accept a payment through Stripe

Based on Accept a Payment Stripe Sample

The core of the library resides in /stripe_api. The other 2 folders contain the following:

• flask_server: A Flask server that exploits this library to accept a payment
• html-client: A HTML & Javascript app that shows how to interact with the server in order to perform a payment

How to use Stripe API?

In order to use the Stripe API you need to perform the following steps:

1. Include the stripe_api package in your application.

2. Use the stripe_api.create_payment_intent() method whenever you need to initialize a new payment as described by the demo Flask Server implemented at /flask_server/server.py

3. Your Frontend Client will need to initialize the payment-

• Basically we need our Frontend client to perform some specific actions so that Stripe is able to trust our Backend server.
• Have a look at the HTML / JS / CSS client implemented within /html_client

4. In order to handle the Stripe Webhook Events that your application needs you have to check the EventTypes currently handled by this API in stripe_api/event.py and adjust accordingly.

   In our case we handle only payment_intent.succeeded, payment_intent.payment_failed and payment_intent.created therefore the EventType class looks like this:

   class EventType(Enum):
       PAYMENT_INTENT_SUCCEEDED = 'payment_intent.succeeded'
       PAYMENT_INTENT_FAILED = 'payment_intent.payment_failed'
       PAYMENT_INTENT_CREATED = 'payment_intent.created'

   If you want to handle a new event type just add a new event to this class, for example:

   class EventType(Enum):
      ...
      PAYMENT_INTENT_CANCELED = 'payment_intent.canceled'

5. Once you decided you want to handle a new event type you have to check current event handlers in stripe_api/handlers.py and adjust accordingly.

   Currently, the package contains handlers only for payment_intent.succeeded, payment_intent.payment_failed and payment_intent.created event types.

   If you want to add a new handler for a new event type, you just need to add a new handling function like this:

   def handle_payment_intent_canceled(webhook_event: Event) -> None:
      logger.debug(f'Payment canceled')   

   And then plug it into the handlers list by associating it with the correct event type:

   handlers = {
      ...
      EventType.PAYMENT_INTENT_CANCELED: handle_payment_intent_canceled
   }

6. After this configuration, you can use the Stripe API as used by the demo Flask Server implemented at /flask_server/server.py

How to Test Stripe API?

Testing the Stripe API is a bit more complex, it requires a full stack app composed by a client and a server in order to emulate the entire payment cycle.

1. Create a webhook using your Stripe account in Test Mode by visiting your Stripe Dashboard > Developers > Webhooks and adding a new webhook with a domain. The domain can be invalid, because we will only use it to forward the events to the local machine.

   Be careful that Stripe automatically deletes webhooks that have an invalid domain, therefore you may need to recreate the webhook once in a while

2. Install Stripe CLI and login by following the following guide

3. Forward the Stripe Webhook Events to your local machine, but select only the events your webhook is able to handle.

   Be careful on how you define your webhook domain and how you forward to your local server. If your webhook domain is https://mytest.ai/webhook and your local server listens at /webhook then your Stripe CLI command should be:

   stripe listen --events payment_intent.created,payment_intent.succeeded,payment_intent.failure --load-from-webhooks-api --forward-to 127.0.0.1:4242

   Note that Stripe CLI will add the missing /webhook to the URL for you

   You should see something like:

    Your webhook signing secret is whsec_8d5d945c60834df9 (^C to quit)

4. Copy the webhook signing secret (whsec_8d5d945c60834df9 in the example above) returned by the Stripe CLI in your environment (or .env file) by setting the STRIPE_WEBHOOK_SECRET variable.

5. Run the Flask server (assuming you are in the project root folder)

   export FLASK_APP=third_party_api/stripe_api/flask_server/server.py
   python3 -m flask run --port=4242
   

6. Visit http://127.0.0.1:4242/ in your browser and perform a payment demo.

• Use the following payment details to test a successful payment.

Card number: 4242 4242 4242 4242
Expiration: 04 / 24
CVV: 242

• change the Card number to 4000 0027 6000 3184 in order to test a card with 3D Secure enabled.

• change the Card number to 4000 0000 0000 0002 in order to test a card that will end up with a Declined Payment.