How to Integrate Stripe Payment Gateway in ASP.NET Core

Integrating Stripe into an ASP.NET Core application follows a consistent pattern regardless of exactly which payment flow you're building: install the official Stripe.net NuGet package, configure your secret key server-side, create a payment intent (or checkout session) on your server, and use the returned client secret on the frontend to confirm the payment through Stripe's own hosted UI or Stripe.js.

The critical architectural rule, worth repeating because it's so easy to get wrong under deadline pressure, is that your Stripe secret key must never appear in any client-side code — it belongs exclusively in server-side configuration, ideally in a secrets store or environment variable rather than committed to appsettings.json in source control. The publishable key, by contrast, is specifically designed to be safe in frontend code.

For a standard checkout flow, your ASP.NET Core controller action creates a Stripe Checkout Session server-side, specifying the line items, success URL, and cancel URL, then returns the session's URL to the frontend, which simply redirects the browser there — Stripe's own hosted checkout page handles collecting card details, so sensitive payment data never touches your own server or codebase at all, which also significantly reduces your PCI compliance burden.

The part of Stripe integration that trips up the most developers isn't the initial checkout flow — it's webhook handling. Stripe sends asynchronous webhook events (payment succeeded, payment failed, subscription renewed) to a URL you configure, and your application needs an endpoint to receive and act on these events, since the checkout redirect alone doesn't guarantee the payment actually completed successfully by the time the user lands back on your site.

Webhook signature verification is the single most commonly skipped security step. Every webhook request includes a Stripe-Signature header, and your endpoint must verify that signature against your webhook signing secret before trusting the payload at all — without this check, anyone who discovers your webhook URL could send fake 'payment succeeded' events directly to your server. Stripe.net provides a dedicated EventUtility.ConstructEvent method specifically for this verification step; skipping it in favor of just deserializing the raw request body is a real, exploitable vulnerability, not just a best-practice suggestion.

Idempotency is worth building in from the start, not retrofitted later — Stripe can, and does, occasionally send the same webhook event more than once due to network retries on their end. Your webhook handler should check whether it's already processed a given event ID before acting on it again, otherwise a duplicate delivery can cause double-fulfillment of an order or a duplicate database update.

Finally, test your entire flow — including webhooks — against Stripe's test mode and test card numbers before ever touching live keys, and use the Stripe CLI's webhook forwarding command during local development, since your local machine isn't reachable at a public URL for Stripe's servers to send real webhook requests to during development otherwise.