diff --git a/README.md b/README.md
index 8faf69be..92dc093f 100644
--- a/README.md
+++ b/README.md
@@ -45,7 +45,7 @@ const server = new ProxyChain.Server({
     // Custom user-defined function to authenticate incoming proxy requests,
     // and optionally provide the URL to chained upstream proxy.
     // The function must return an object (or promise resolving to the object) with the following signature:
-    // { requestAuthentication: Boolean, upstreamProxyUrl: String }
+    // { requestAuthentication: boolean, upstreamProxyUrl: string, failMsg?: string, customTag?: unknown }
     // If the function is not defined or is null, the server runs in simple mode.
     // Note that the function takes a single argument with the following properties:
     // * request      - An instance of http.IncomingMessage class with information about the client request
@@ -72,6 +72,12 @@ const server = new ProxyChain.Server({
             // If "requestAuthentication" is true, you can use the following property
             // to define a custom error message to return to the client instead of the default "Proxy credentials required"
             failMsg: 'Bad username or password, please try again.',
+
+            // Optional custom tag that will be passed back via
+            // `tunnelConnectResponded` or `tunnelConnectFailed` events
+            // Can be used to pass information between proxy-chain
+            // and any external code or application using it
+            customTag: { userId: '123' },
         };
     },
 });
@@ -326,7 +332,7 @@ the parameter types of the event callback are described in [Node.js's documentat
 [1]: https://nodejs.org/api/http.html#http_event_connect
 
 ```javascript
-server.on('tunnelConnectResponded', ({ proxyChainId, response, socket, head }) => {
+server.on('tunnelConnectResponded', ({ proxyChainId, response, socket, head, customTag }) => {
     console.log(`CONNECT response headers received: ${response.headers}`);
 });
 ```
@@ -339,6 +345,14 @@ listenConnectAnonymizedProxy(anonymizedProxyUrl, ({ response, socket, head }) =>
 });
 ```
 
+You can also listen to CONNECT requests that receive response with status code different from 200.
+The proxy server would emit a `tunnelConnectFailed` event.
+
+```javascript
+server.on('tunnelConnectFailed', ({ proxyChainId, response, socket, head, customTag }) => {
+    console.log(`CONNECT response failed with status code: ${response.statusCode}`);
+});
+```
 
 ## Helper functions
 
diff --git a/package.json b/package.json
index abbb0a60..7417a5f6 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "proxy-chain",
-  "version": "2.2.1",
+  "version": "2.3.0",
   "description": "Node.js implementation of a proxy server (think Squid) with support for SSL, authentication, upstream proxy chaining, and protocol tunneling.",
   "main": "dist/index.js",
   "keywords": [
diff --git a/src/chain.ts b/src/chain.ts
index 9f70cbb6..f9a07545 100644
--- a/src/chain.ts
+++ b/src/chain.ts
@@ -33,6 +33,7 @@ export interface HandlerOpts {
     localAddress?: string;
     ipFamily?: number;
     dnsLookup?: typeof dns['lookup'];
+    customTag?: unknown;
 }
 
 interface ChainOpts {
@@ -72,7 +73,7 @@ export const chain = (
 
     const { proxyChainId } = sourceSocket;
 
-    const { upstreamProxyUrlParsed: proxy } = handlerOpts;
+    const { upstreamProxyUrlParsed: proxy, customTag } = handlerOpts;
 
     const options: Options = {
         method: 'CONNECT',
@@ -127,6 +128,14 @@ export const chain = (
                 sourceSocket.end(createHttpResponse(status, `UPSTREAM${response.statusCode}`));
             }
 
+            server.emit('tunnelConnectFailed', {
+                proxyChainId,
+                response,
+                customTag,
+                socket: targetSocket,
+                head: clientHead,
+            });
+
             return;
         }
 
@@ -138,6 +147,7 @@ export const chain = (
         server.emit('tunnelConnectResponded', {
             proxyChainId,
             response,
+            customTag,
             socket: targetSocket,
             head: clientHead,
         });
diff --git a/src/server.ts b/src/server.ts
index b0387651..b4fe8f52 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -52,6 +52,7 @@ type HandlerOpts = {
     localAddress?: string;
     ipFamily?: number;
     dnsLookup?: typeof dns['lookup'];
+    customTag?: unknown;
 };
 
 export type PrepareRequestFunctionOpts = {
@@ -73,6 +74,7 @@ export type PrepareRequestFunctionResult = {
     localAddress?: string;
     ipFamily?: number;
     dnsLookup?: typeof dns['lookup'];
+    customTag?: unknown;
 };
 
 type Promisable<T> = T | Promise<T>;
@@ -419,6 +421,7 @@ export class Server extends EventEmitter {
         handlerOpts.ipFamily = funcResult.ipFamily;
         handlerOpts.dnsLookup = funcResult.dnsLookup;
         handlerOpts.customConnectServer = funcResult.customConnectServer;
+        handlerOpts.customTag = funcResult.customTag;
 
         // If not authenticated, request client to authenticate
         if (funcResult.requestAuthentication) {