From 5c29d02fa731fafce6b76e35f78b2f165b887246 Mon Sep 17 00:00:00 2001
From: Chris Park <chris.park@aligent.com.au>
Date: Wed, 1 Nov 2023 10:20:13 +1030
Subject: [PATCH 1/2] DO-1563: Add custom header to forward user-agent header
 value to the Prerender origin

---
 packages/prerender-proxy/lib/handlers/prerender-check.ts | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/packages/prerender-proxy/lib/handlers/prerender-check.ts b/packages/prerender-proxy/lib/handlers/prerender-check.ts
index 879c1d25..6ab03ad3 100644
--- a/packages/prerender-proxy/lib/handlers/prerender-check.ts
+++ b/packages/prerender-proxy/lib/handlers/prerender-check.ts
@@ -26,6 +26,14 @@ export const handler = async (
       request.headers["x-prerender-host"] = [
         { key: "X-Prerender-Host", value: request.headers.host[0].value },
       ];
+
+      // Custom header to be forwarded to Prerender service for better logging
+      request.headers["x-prerender-user-agent"] = [
+        {
+          key: "x-prerender-user-agent",
+          value: request.headers["user-agent"][0].value,
+        },
+      ];
     }
   }
 

From c1db14864c01aef5cb04210d4ffc9305b829322d Mon Sep 17 00:00:00 2001
From: Chris Park <chris.park@aligent.com.au>
Date: Wed, 1 Nov 2023 10:31:03 +1030
Subject: [PATCH 2/2] DO-1563: Log custom header having the Prerender
 requester's User-Agent information

---
 packages/prerender-fargate/lib/prerender/server.js | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/packages/prerender-fargate/lib/prerender/server.js b/packages/prerender-fargate/lib/prerender/server.js
index d7a41ef1..587a7667 100644
--- a/packages/prerender-fargate/lib/prerender/server.js
+++ b/packages/prerender-fargate/lib/prerender/server.js
@@ -23,10 +23,13 @@ const server = prerender({
 
 server.use({
     requestReceived: (req, res, next) => {
-        console.log(`${new Date().toISOString()} User-Agent: "${req.get('user-agent')}" ${req.prerender.reqId} ${req.prerender.url}`);
+        // Log "x-prerender-user-agent" value forwarded from CloudFront/Lambda@edge that contains the original User-Agent value. If not present, e.g. requests from ELB, default to "user-agent" value.
+        const userAgent = req.get('x-prerender-user-agent') || req.get('user-agent');
+
+        console.log(`${new Date().toISOString()} User-Agent: "${userAgent}" ${req.prerender.reqId} ${req.prerender.url}`);
         let auth = req.headers['x-prerender-token'];
         if (!auth) {
-            console.log(`${new Date().toISOString()} "${req.get('user-agent')}" ${req.prerender.reqId} Authentication header not found.`);
+            console.log(`${new Date().toISOString()} "${userAgent}" ${req.prerender.reqId} Authentication header not found.`);
             return res.send(401);
         }
 
@@ -40,7 +43,7 @@ server.use({
             if (authenticated) break;
         }
         if (!authenticated) {
-            console.log(`${new Date().toISOString()} "${req.get('user-agent')}" ${req.prerender.reqId} Authentication Failed.`);
+            console.log(`${new Date().toISOString()} "${userAgent}" ${req.prerender.reqId} Authentication Failed.`);
             return res.send(401);
         }