Sometimes you want to subscribe to changes from an API, and we don’t have an Integration for it yet. That’s when you can use defineHttpEndpoint to receive webhooks, verify them, and create an HTTP Trigger. You should read the HTTP endpoint documentation to understand how to create an HTTP endpoint.

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Examples

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Cal.com

Cal.com has webhooks that closely follow conventions, and so are easy to use.
Cal.com
//create an HTTP endpoint
const caldotcom = client.defineHttpEndpoint({
  id: "cal.com",
  source: "cal.com",
  icon: "caldotcom",
  verify: async (request) => {
    //this helper function makes verifying most webhooks easy
    return await verifyRequestSignature({
      request,
      headerName: "X-Cal-Signature-256",
      secret: process.env.CALDOTCOM_SECRET!,
      algorithm: "sha256",
    });
  },
});

client.defineJob({
  id: "http-caldotcom",
  name: "HTTP Cal.com",
  version: "1.0.0",
  enabled: true,
  //create a Trigger from the HTTP endpoint above. The filter is optional.
  trigger: caldotcom.onRequest({ filter: { body: { triggerEvent: ["BOOKING_CANCELLED"] } } }),
  run: async (request, io, ctx) => {
    //note that when using HTTP endpoints, the first parameter is the request
    //you need to get the body, usually it will be json so you do:
    const body = await request.json();
    await io.logger.info(`Body`, body);
  },
});

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WhatsApp

WhatsApp is more unusual. When you enter the webhook URL and secret into the Meta developer dashboard, they send a GET request that requires a specific Response. We can handle this though, by using the respondWith option. This allows us to define a function that will be called immediately when a Request is received. The filter ensures we only receive GET requests with a specific query parameter. Then in the handler we response appropriately if the hub.verify_token matches our secret. 
const whatsApp = client.defineHttpEndpoint({
  id: "whatsapp",
  source: "whatsapp.com",
  icon: "whatsapp",
  //only needed for strange APIs like WhatsApp which don't setup the webhook until you pass the test
  respondWith: {
    //we don't want to trigger Runs for the verification `GET` request
    skipTriggeringRuns: true,
    //we only want to respond to `GET` requests with a specific query parameter
    filter: {
      method: ["GET"],
      query: {
        "hub.mode": [{ $startsWith: "sub" }],
      },
    },
    handler: async (request, verify) => {
      const searchParams = new URL(request.url).searchParams;
      if (searchParams.get("hub.verify_token") !== process.env.WHATSAPP_WEBHOOK_SECRET) {
        return new Response("Unauthorized", { status: 401 });
      }
      return new Response(searchParams.get("hub.challenge") ?? "OK", { status: 200 });
    },
  },
  verify: async (request) => {
    //verification of the actual webhooks is easy
    return await verifyRequestSignature({
      request,
      headerName: "x-hub-signature-256",
      secret: process.env.WHATSAPP_APP_SECRET!,
      algorithm: "sha256",
    });
  },
});

client.defineJob({
  id: "http-whatsapp",
  name: "HTTP WhatsApp",
  version: "1.1.0",
  enabled: true,
  //create a Trigger from the HTTP endpoint above. You can provide an optional filter.
  trigger: whatsApp.onRequest(),
  run: async (request, io, ctx) => {
    //note that when using HTTP endpoints, the first parameter is the request
    //you need to get the body, usually it will be json so you do:
    const body = await request.json();
    await io.logger.info(`Body`, body);
  },
});