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fix: webhook verification using a constant-time comparison (#2)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,52 @@ | ||
| export async function verifyWebhookSignature(payload, signature, secret) { | ||
| if (!signature) { | ||
| throw new Error("Signature is missing"); | ||
| } else if (!signature.startsWith("sha256=")) { | ||
| throw new Error("Invalid signature format"); | ||
| } | ||
|
|
||
| const algorithm = { name: "HMAC", hash: "SHA-256" }; | ||
| const enc = new TextEncoder(); | ||
| const key = await crypto.subtle.importKey( | ||
| "raw", | ||
| enc.encode(secret), | ||
| algorithm, | ||
| false, | ||
| ["sign", "verify"] | ||
| ); | ||
|
|
||
| const signed = await crypto.subtle.sign( | ||
| algorithm.name, | ||
| key, | ||
| enc.encode(payload) | ||
| ); | ||
| const expectedSignature = "sha256=" + array2hex(signed); | ||
| if (!safeCompare(expectedSignature, signature)) { | ||
| throw new Error("Signature does not match event payload and secret"); | ||
| } | ||
|
|
||
| // All good! | ||
| } | ||
|
|
||
| function array2hex(arr) { | ||
| return [...new Uint8Array(arr)] | ||
| .map((x) => x.toString(16).padStart(2, "0")) | ||
| .join(""); | ||
| } | ||
|
|
||
| /** Constant-time string comparison */ | ||
| function safeCompare(expected, actual) { | ||
| const lenExpected = expected.length; | ||
| let result = 0; | ||
|
|
||
| if (lenExpected !== actual.length) { | ||
| actual = expected; | ||
| result = 1; | ||
| } | ||
|
|
||
| for (let i = 0; i < lenExpected; i++) { | ||
| result |= expected.charCodeAt(i) ^ actual.charCodeAt(i); | ||
| } | ||
|
|
||
| return result === 0; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,97 +1,102 @@ | ||
| const { App } = require("@octokit/app"); | ||
| import { App } from "@octokit/app"; | ||
| import { verifyWebhookSignature } from "./lib/verify.js"; | ||
|
|
||
| // wrangler secret put APP_ID | ||
| const appId = APP_ID; | ||
| // wrangler secret put WEBHOOK_SECRET | ||
| const secret = WEBHOOK_SECRET; | ||
| export default { | ||
| /** | ||
| * @param {Request} request | ||
| * @param {Record<string, any>} env | ||
| */ | ||
| async fetch(request, env) { | ||
|
|
||
| // The private-key.pem file from GitHub needs to be transformed from the | ||
| // PKCS#1 format to PKCS#8, as the crypto APIs do not support PKCS#1: | ||
| // | ||
| // openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in private-key.pem -out private-key-pkcs8.pem | ||
| // | ||
| // The private key is too large, so we split it up across 3 keys. | ||
| // You can split up the *.pem file into 3 equal parts with | ||
| // | ||
| // split -l 10 private-key-pkcs8.pem | ||
| // | ||
| // Then set the priveat keys | ||
| // | ||
| // cat xaa | wrangler secret put PRIVATE_KEY_1 | ||
| // cat xab | wrangler secret put PRIVATE_KEY_2 | ||
| // cat xac | wrangler secret put PRIVATE_KEY_3 | ||
| // | ||
| const privateKey = [PRIVATE_KEY_1, PRIVATE_KEY_2, PRIVATE_KEY_3].join("\n"); | ||
| // wrangler secret put APP_ID | ||
| const appId = env.APP_ID; | ||
| // wrangler secret put WEBHOOK_SECRET | ||
| const secret = env.WEBHOOK_SECRET; | ||
|
|
||
| // instantiate app | ||
| // https://github.com/octokit/app.js/#readme | ||
| const app = new App({ | ||
| appId, | ||
| privateKey, | ||
| webhooks: { | ||
| secret, | ||
| }, | ||
| }); | ||
| // The private-key.pem file from GitHub needs to be transformed from the | ||
| // PKCS#1 format to PKCS#8, as the crypto APIs do not support PKCS#1: | ||
| // | ||
| // openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in private-key.pem -out private-key-pkcs8.pem | ||
| // | ||
| // Then set the private key | ||
| // | ||
| // cat private-key-pkcs8.pem | wrangler secret put PRIVATE_KEY | ||
| // | ||
| const privateKey = env.PRIVATE_KEY; | ||
|
|
||
| app.webhooks.on("issues.opened", async ({ octokit, payload }) => { | ||
| await octokit.request( | ||
| "POST /repos/{owner}/{repo}/issues/{issue_number}/comments", | ||
| { | ||
| owner: payload.repository.owner.login, | ||
| repo: payload.repository.name, | ||
| issue_number: payload.issue.number, | ||
| body: | ||
| "Hello there from [Cloudflare Workers](https://github.com/gr2m/cloudflare-worker-github-app-example/#readme)", | ||
| } | ||
| ); | ||
| }); | ||
| // instantiate app | ||
| // https://github.com/octokit/app.js/#readme | ||
| const app = new App({ | ||
| appId, | ||
| privateKey, | ||
| webhooks: { | ||
| secret, | ||
| }, | ||
| }); | ||
|
|
||
| addEventListener("fetch", (event) => { | ||
| event.respondWith(handleRequest(event.request)); | ||
| }); | ||
| app.webhooks.on("issues.opened", async ({ octokit, payload }) => { | ||
| await octokit.request( | ||
| "POST /repos/{owner}/{repo}/issues/{issue_number}/comments", | ||
| { | ||
| owner: payload.repository.owner.login, | ||
| repo: payload.repository.name, | ||
| issue_number: payload.issue.number, | ||
| body: | ||
| "Hello there from [Cloudflare Workers](https://github.com/gr2m/cloudflare-worker-github-app-example/#readme)", | ||
| } | ||
| ); | ||
| }); | ||
|
|
||
| /** | ||
| * Respond with hello worker text | ||
| * @param {Request} request | ||
| */ | ||
| async function handleRequest(request) { | ||
| if (request.method === "GET") { | ||
| const { data } = await app.octokit.request("GET /app"); | ||
| if (request.method === "GET") { | ||
| const { data } = await app.octokit.request("GET /app"); | ||
|
|
||
| return new Response( | ||
| `<h1>Cloudflare Worker Example GitHub app</h1> | ||
| return new Response( | ||
| `<h1>Cloudflare Worker Example GitHub app</h1> | ||
| <p>Installation count: ${data.installations_count}</p> | ||
| <p><a href="https://github.com/apps/cloudflare-worker-example">Install</a> | <a href="https://github.com/gr2m/cloudflare-worker-github-app-example/#readme">source code</a></p>`, | ||
| { | ||
| headers: { "content-type": "text/html" }, | ||
| } | ||
| ); | ||
| } | ||
| { | ||
| headers: { "content-type": "text/html" }, | ||
| } | ||
| ); | ||
| } | ||
|
|
||
| const id = request.headers.get("x-github-delivery"); | ||
| const name = request.headers.get("x-github-event"); | ||
| const payload = await request.json(); | ||
| const id = request.headers.get("x-github-delivery"); | ||
| const name = request.headers.get("x-github-event"); | ||
| const signature = request.headers.get("x-hub-signature-256") ?? ""; | ||
| const payloadString = await request.text(); | ||
| const payload = JSON.parse(payloadString); | ||
|
|
||
| try { | ||
| // TODO: implement signature verification | ||
| // https://github.com/gr2m/cloudflare-worker-github-app-example/issues/1 | ||
| await app.webhooks.receive({ | ||
| id, | ||
| name, | ||
| payload, | ||
| }); | ||
| // Verify webhook signature | ||
| try { | ||
| await verifyWebhookSignature(payloadString, signature, secret); | ||
| } catch (error) { | ||
| app.log.warn(error.message); | ||
| return new Response(`{ "error": "${error.message}" }`, { | ||
| status: 400, | ||
| headers: { "content-type": "application/json" }, | ||
| }); | ||
| } | ||
|
|
||
| return new Response(`{ "ok": true }`, { | ||
| headers: { "content-type": "application/json" }, | ||
| }); | ||
| } catch (error) { | ||
| app.log.error(error); | ||
| // Now handle the request | ||
| try { | ||
| await app.webhooks.receive({ | ||
| id, | ||
| name, | ||
| payload, | ||
| }); | ||
|
|
||
| return new Response(`{ "error": "${error.message}" }`, { | ||
| status: 500, | ||
| headers: { "content-type": "application/json" }, | ||
| }); | ||
| } | ||
| } | ||
| return new Response(`{ "ok": true }`, { | ||
| headers: { "content-type": "application/json" }, | ||
| }); | ||
| } catch (error) { | ||
| app.log.error(error); | ||
|
|
||
| return new Response(`{ "error": "${error.message}" }`, { | ||
| status: 500, | ||
| headers: { "content-type": "application/json" }, | ||
| }); | ||
| } | ||
| }, | ||
| }; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,6 +1,5 @@ | ||
| name = "github-app-example" | ||
| type = "webpack" | ||
| account_id = "f8d9cac88285c4d654ba305a92e952d6" | ||
| workers_dev = true | ||
| route = "" | ||
| zone_id = "" | ||
|
|
||
| main = "worker.js" |