diff --git a/README.md b/README.md
index 8561a9c..dc80847 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,14 @@ heroku config:add PATH_PREFIX=/awesome/symbols
 
 Now the symbol server URL can be `http://pepto-symbol.gadgetron.com`.
 
+### Optional S3 request signing
+
+When running against a private S3 origin, the server can sign outgoing `GET` requests.
+
+- Signing is enabled automatically when both `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` are present.
+- `AWS_REGION` is required when signing is enabled.
+- `AWS_SESSION_TOKEN` is optional, you can use it for [temporary credentials](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_use-resources.html).
+
 ### Running locally
 
 To run Pepto Symbol locally on port 5000:
diff --git a/package.json b/package.json
index b2a5fa7..b103618 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
     "node": ">=14"
   },
   "dependencies": {
+    "aws4": "^1.13.2",
     "http-proxy": "^1.18.1",
     "lru-cache": "^6.0.0",
     "uuid": "^8.3.2"
@@ -16,6 +17,7 @@
     "start:dev": "PATH_PREFIX=/atom-shell/symbols S3_BUCKET=gh-contractor-zcbenz npm start"
   },
   "devDependencies": {
+    "@types/aws4": "^1.11.6",
     "@types/http-proxy": "^1.17.6",
     "@types/lru-cache": "^5.1.0",
     "@types/node": "^15.6.1",
diff --git a/src/index.ts b/src/index.ts
index c01c99a..5bb517e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,4 +1,5 @@
 import assert from 'assert';
+import aws4 from 'aws4';
 import * as http from 'http';
 import httpProxy from 'http-proxy';
 import LRU from 'lru-cache';
@@ -39,6 +40,20 @@ const missingSymbolCache = new LRU<string, boolean>({
   max: 10000,
 });
 
+const signingAccessKeyId = process.env.AWS_ACCESS_KEY_ID;
+const signingSecretAccessKey = process.env.AWS_SECRET_ACCESS_KEY;
+const signingSessionToken = process.env.AWS_SESSION_TOKEN;
+const signingRegion = process.env.AWS_REGION;
+const shouldSignS3Requests = Boolean(signingAccessKeyId && signingSecretAccessKey);
+
+assert(!shouldSignS3Requests || signingRegion, 'AWS_REGION is defined when S3 request signing is enabled');
+
+type ProxyRequest = http.IncomingMessage & {
+  proxyPath?: string;
+  cacheKey?: string;
+  proxyMethod?: string;
+};
+
 function incomingPathToProxyPath(path: string): string {
   // symstore.exe and symsrv.dll don't always agree on the case of the path to a
   // given symbol file. Since our artifact URLs are case-sensitive, this causes symbol
@@ -58,11 +73,54 @@ function incomingPathToProxyPath(path: string): string {
 
   // The symbols may be hosted a deeper path in the artifact store
   // so we prefix the incoming path with that prefix
-  return `${PATH_PREFIX || ''}${newPath}`;
+  if (!PATH_PREFIX) {
+    return newPath;
+  }
+
+  // Handle cases where PATH_PREFIX or newPath may or may not have a
+  // leading/trailing slash to avoid double slashes or missing slashes
+  if (PATH_PREFIX.endsWith('/') && newPath.startsWith('/')) {
+    return `${PATH_PREFIX.slice(0, -1)}${newPath}`;
+  }
+
+  // Handle cases where PATH_PREFIX may or may not have a trailing slash
+  // and newPath may or may not have a leading slash
+  if (!PATH_PREFIX.endsWith('/') && !newPath.startsWith('/')) {
+    return `${PATH_PREFIX}/${newPath}`;
+  }
+
+  return `${PATH_PREFIX}${newPath}`;
+}
+
+function signS3ProxyPath(path: string, method: string): string {
+  if (!shouldSignS3Requests) {
+    return path;
+  }
+
+  const targetUrl = new url.URL(path, TARGET_URL);
+  const signedRequest = aws4.sign({
+    host: TARGET_HOST!,
+    method,
+    service: 's3',
+    region: signingRegion!,
+    signQuery: true,
+    path: `${targetUrl.pathname}${targetUrl.search}`,
+  }, {
+    accessKeyId: signingAccessKeyId!,
+    secretAccessKey: signingSecretAccessKey!,
+    sessionToken: signingSessionToken,
+  });
+
+  return signedRequest.path || `${targetUrl.pathname}${targetUrl.search}`;
 }
 
 proxy.on('proxyReq', (proxyReq, request, response, options) => {
-  proxyReq.path = incomingPathToProxyPath(proxyReq.path);
+  const req = request as ProxyRequest;
+  const proxyPath = req.proxyPath ?? incomingPathToProxyPath(proxyReq.path);
+  const cacheKey = req.cacheKey ?? incomingPathToProxyPath(proxyReq.path);
+  const proxyMethod = req.proxyMethod ?? proxyReq.method;
+
+  proxyReq.path = proxyPath;
 
   // AZ CDN determines the bucket from the Host header
   proxyReq.setHeader('Host', TARGET_HOST);
@@ -75,12 +133,17 @@ proxy.on('proxyReq', (proxyReq, request, response, options) => {
   // convert 403s to 404s so symsrv.dll doesn't freak out.
   const originalWriteHead = response.writeHead;
   response.writeHead = (...args: [number, any]) => {
-    if (args[0] == 403) {
-      missingSymbolCache.set(proxyReq.path, true);
+    if (proxyMethod === 'GET') {
+      if (args[0] == 403) {
+        missingSymbolCache.set(cacheKey, true);
+        args[0] = 404;
+      } else {
+        missingSymbolCache.set(cacheKey, false);
+      }
+    } else if (args[0] == 403) {
       args[0] = 404;
-    } else {
-      missingSymbolCache.set(proxyReq.path, false);
     }
+
     return originalWriteHead.apply(response, args);
   };
 });
@@ -104,16 +167,21 @@ http.createServer((req, res) => {
   }
 
   const cacheKey = incomingPathToProxyPath(parsed.pathname + parsed.search);
+  const requestMethod = (req.method || 'GET').toUpperCase();
   const userAgent = req.headers['user-agent'];
   const isSentryRequest = userAgent && userAgent.startsWith('symbolicator/');
 
+  let signedProxyPath: string;
+  try {
+    signedProxyPath = signS3ProxyPath(cacheKey, requestMethod);
+  } catch (error) {
+    const errorId = uuid.v4();
+    console.error('Signing Error:', errorId, 'Request:', req.url, error);
+    return res.writeHead(500).end(`Failed to sign S3 request. If this happens consistently please report to https://github.com/electron/symbol-server with this error ID: "${errorId}"`);
+  }
+
   if (isSentryRequest || req.headers['x-electron-symbol-redirect'] === '1') {
-    res.setHeader('Location', url.format({
-      protocol: 'https:',
-      slashes: true,
-      host: TARGET_HOST,
-      pathname: cacheKey,
-    }));
+    res.setHeader('Location', `${TARGET_URL}${signedProxyPath}`);
     return res.writeHead(302).end();
   }
 
@@ -121,6 +189,11 @@ http.createServer((req, res) => {
     return res.writeHead(404).end();
   }
 
+  const proxyReq = req as ProxyRequest;
+  proxyReq.cacheKey = cacheKey;
+  proxyReq.proxyPath = signedProxyPath;
+  proxyReq.proxyMethod = requestMethod;
+
   proxy.web(req, res, { target: TARGET_URL });
 }).listen(process.env.PORT || 8080);
 
diff --git a/yarn.lock b/yarn.lock
index e0eb57b..e018456 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9,10 +9,12 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@electron/symbol-server@workspace:."
   dependencies:
+    "@types/aws4": "npm:^1.11.6"
     "@types/http-proxy": "npm:^1.17.6"
     "@types/lru-cache": "npm:^5.1.0"
     "@types/node": "npm:^15.6.1"
     "@types/uuid": "npm:^8.3.0"
+    aws4: "npm:^1.13.2"
     http-proxy: "npm:^1.18.1"
     lru-cache: "npm:^6.0.0"
     typescript: "npm:^4.3.2"
@@ -20,6 +22,15 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@types/aws4@npm:^1.11.6":
+  version: 1.11.6
+  resolution: "@types/aws4@npm:1.11.6"
+  dependencies:
+    "@types/node": "npm:*"
+  checksum: 10c0/abb84d0dad0b791124389b1bfd2c4c2813077af162cac128f1eb0793f0d4fe3084aa1168f62b41e39f80730aa45b95a9a0034f85c254bebf2194721fe02bc9ad
+  languageName: node
+  linkType: hard
+
 "@types/http-proxy@npm:^1.17.6":
   version: 1.17.6
   resolution: "@types/http-proxy@npm:1.17.6"
@@ -57,6 +68,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"aws4@npm:^1.13.2":
+  version: 1.13.2
+  resolution: "aws4@npm:1.13.2"
+  checksum: 10c0/c993d0d186d699f685d73113733695d648ec7d4b301aba2e2a559d0cd9c1c902308cc52f4095e1396b23fddbc35113644e7f0a6a32753636306e41e3ed6f1e79
+  languageName: node
+  linkType: hard
+
 "eventemitter3@npm:^4.0.0":
   version: 4.0.4
   resolution: "eventemitter3@npm:4.0.4"