fix: Add Flagsmith signature header when testing webhook.

Fixes #2786.
We are trying to create the same signature as the webhook
in the python code. This commit assumes that the python code
will use the same approach to create signature for long term.

api/core/signing.py

@@ -3,6 +3,8 @@
 
 
 def sign_payload(payload: str, key: str):
+    # signPayload of frontend/web/components/TestWebHook on the frontend replicates this
+    # exact function, change the function there if this changes.
     return hmac.new(
         key=key.encode(), msg=payload.encode(), digestmod=hashlib.sha256
     ).hexdigest()

api/edge_api/identities/edge_request_forwarder.py

@@ -81,6 +81,9 @@ def _get_headers(request_method: str, headers: dict, payload: str = "") -> dict:
     # ref: https://groups.google.com/g/django-developers/c/xjYVJN-RguA/m/G9krDqawchQJ
     if request_method == "GET":
         headers.pop("Content-Length", None)
+
+    # TestWebHook on the frontend replicates this exact function, change the
+    # function there if this changes.
     signature = sign_payload(payload, settings.EDGE_REQUEST_SIGNING_KEY)
     headers[FLAGSMITH_SIGNATURE_HEADER] = signature
     return headers

api/webhooks/webhooks.py

@@ -153,6 +153,8 @@ def _call_webhook(
     headers = {"content-type": "application/json"}
     json_data = json.dumps(data, sort_keys=True, cls=DjangoJSONEncoder)
     if webhook.secret:
+        # TestWebHook on the frontend replicates this exact function, change the
+        # function there if this changes.
         signature = sign_payload(json_data, key=webhook.secret)
         headers.update({FLAGSMITH_SIGNATURE_HEADER: signature})
 
@@ -199,6 +201,8 @@ def call_webhook_with_failure_mail_after_retries(
     headers = {"content-type": "application/json"}
     json_data = json.dumps(data, sort_keys=True, cls=DjangoJSONEncoder)
     if webhook.secret:
+        # TestWebHook on the frontend replicates this exact function, change the
+        # function there if this changes.
         signature = sign_payload(json_data, key=webhook.secret)
         headers.update({FLAGSMITH_SIGNATURE_HEADER: signature})
 

frontend/web/components/TestWebhook.tsx

@@ -8,34 +8,79 @@ import Button from './base/forms/Button'
 type TestWebhookType = {
   webhook: string
   json: string
+  secret: string
 }
 
-const TestWebhook: FC<TestWebhookType> = ({ json, webhook }) => {
+// from https://stackoverflow.com/questions/24834812/space-in-between-json-stringify-output
+const stringifyWithSpaces = (str: string) => {
+  const obj = JSON.parse(str)
+  let result = JSON.stringify(obj, null, 1) // stringify, with line-breaks and indents
+  result = result.replace(/^ +/gm, ' ') // remove all but the first space for each line
+  result = result.replace(/\n/g, '') // remove line-breaks
+  result = result.replace(/{ /g, '{').replace(/ }/g, '}') // remove spaces between object-braces and first/last props
+  result = result.replace(/\[ /g, '[').replace(/ \]/g, ']') // remove spaces between array-brackets and first/last items
+  return result
+}
+
+const signPayload = async (body: string, secret: string): Promise<string> => {
+  const enc = new TextEncoder()
+
+  const key = await window.crypto.subtle.importKey(
+    'raw',
+    enc.encode(secret),
+    {
+      hash: { name: 'SHA-256' },
+      name: 'HMAC',
+    },
+    false,
+    ['sign'],
+  )
+
+  const signature = await window.crypto.subtle.sign(
+    'HMAC',
+    key,
+    enc.encode(stringifyWithSpaces(body)), // We do this bc the python output is single line with one space before each value
+  )
+  const signatureUnsignedIntArray = new Uint8Array(signature)
+  return Array.prototype.map
+    .call(signatureUnsignedIntArray, (element) =>
+      element.toString(16).padStart(2, '0'),
+    )
+    .join('')
+}
+
+const TestWebhook: FC<TestWebhookType> = ({ json, secret, webhook }) => {
   const [error, setError] = useState<string | null>(null)
   const [loading, setLoading] = useState(false)
   const [success, setSuccess] = useState(false)
+
   const submit = () => {
     setError(null)
     setLoading(true)
     setSuccess(false)
-    data
-      .post(webhook, JSON.parse(json), null)
-      .then(() => {
-        setLoading(false)
-        setSuccess(true)
-      })
-      .catch((e) => {
-        if (e.text) {
-          e.text().then((error: string) => {
-            setError(`The server returned an error: ${error}`)
-          })
-        } else {
-          setError('There was an error posting to your webhook.')
-        }
-      })
-      .finally(() => {
-        setLoading(false)
-      })
+    signPayload(json, secret).then((sign) => {
+      const headers = {
+        'X-Flagsmith-Signature': sign,
+      }
+      data
+        .post(webhook, JSON.parse(json), headers)
+        .then(() => {
+          setLoading(false)
+          setSuccess(true)
+        })
+        .catch((e) => {
+          if (e.text) {
+            e.text().then((error: string) => {
+              setError(`The server returned an error: ${error}`)
+            })
+          } else {
+            setError('There was an error posting to your webhook.')
+          }
+        })
+        .finally(() => {
+          setLoading(false)
+        })
+    })
   }
   return (
     <div>

frontend/web/components/modals/CreateAuditWebhook.js

@@ -133,6 +133,7 @@ const CreateAuditWebhook = class extends Component {
                     <TestWebhook
                       json={Constants.exampleAuditWebhook}
                       webhook={this.state.url}
+                      secret={this.state.secret}
                     />
                     {isEdit ? (
                       <Button

frontend/web/components/modals/CreateWebhook.js

@@ -139,6 +139,7 @@ const CreateWebhook = class extends Component {
                     <TestWebhook
                       json={Constants.exampleWebhook}
                       webhook={this.state.url}
+                      secret={this.state.secret}
                     />
                     {isEdit ? (
                       <Button