Fix test_host_header_security to use httpbin.org for reliable testing (#82)

Replace flaky Cloudflare-based test with httpbin.org/headers which reliably
echoes back received headers. This allows us to directly verify that httpjail
corrects mismatched Host headers without depending on external service
blocking behavior (which was inconsistent across datacenters).

The new approach:
1. Tests what we control: httpjail's Host header correction
2. Uses reliable service: httpbin.org simply echoes headers
3. Has clear assertions: directly checks Host header values
4. No flakiness: doesn't rely on varying security policies

Fixes the test failure that occurred because Cloudflare stopped consistently
blocking mismatched Host headers (error 1034).

Author: ammar-agent

tests/weak_integration.rs

@@ -290,60 +290,74 @@ fn test_server_mode() {
 
 /// Test for Host header security (Issue #57)
 /// Verifies that httpjail corrects mismatched Host headers to prevent
-/// CloudFlare and other CDN routing bypasses.
+/// CDN routing bypasses and other Host header attacks.
+///
+/// This test uses httpbin.org/headers which echoes back the received headers,
+/// allowing us to verify that httpjail corrects the Host header to match the
+/// actual destination URL rather than relying on external service blocking behavior.
 #[test]
 fn test_host_header_security() {
     use std::process::Command;
 
-    // Test with Cloudflare's trace endpoint that clearly shows the Host header
-    let curl_args = vec![
-        "-s",
-        "-H",
-        "Host: evil.com",
-        "--max-time",
-        "3",
-        "http://www.cloudflare.com/cdn-cgi/trace",
-    ];
-
-    // Test 1: Direct curl execution (without httpjail) - Cloudflare blocks mismatched Host
+    // Test 1: Direct curl with mismatched Host header
+    // httpbin.org/headers echoes back all headers it receives
     let direct_result = Command::new("curl")
-        .args(&curl_args)
+        .args([
+            "-s",
+            "-H",
+            "Host: evil.com",
+            "--max-time",
+            "5",
+            "http://httpbin.org/headers",
+        ])
         .output()
         .expect("Failed to execute curl directly");
 
     let direct_stdout = String::from_utf8_lossy(&direct_result.stdout);
-    // Cloudflare returns an error code (1034) for mismatched Host headers
+
+    // Verify curl sends the mismatched Host header as-is
     assert!(
-        direct_stdout.contains("error code: 1034"),
-        "Direct curl with mismatched Host header should be blocked by Cloudflare with error 1034 (got: {})",
+        direct_stdout.contains("\"Host\": \"evil.com\"")
+            || direct_stdout.contains("\"Host\":\"evil.com\""),
+        "Direct curl should send mismatched Host header (got: {})",
         direct_stdout
     );
 
     // Test 2: Same curl command through httpjail - should correct the Host header
     let httpjail_result = HttpjailCommand::new()
         .weak()
         .js("true") // Allow all requests
-        .command(vec!["curl"].into_iter().chain(curl_args.clone()).collect())
+        .command(vec![
+            "curl",
+            "-s",
+            "-H",
+            "Host: evil.com",
+            "--max-time",
+            "5",
+            "http://httpbin.org/headers",
+        ])
         .execute();
 
     assert!(httpjail_result.is_ok(), "Httpjail request should complete");
     let (exit_code, stdout, _) = httpjail_result.unwrap();
     assert_eq!(exit_code, 0, "Httpjail request should succeed");
 
-    // Httpjail should have corrected the Host header, allowing the request to succeed
+    // Verify httpjail corrected the Host header to match the actual destination
     assert!(
-        stdout.contains("h=www.cloudflare.com"),
-        "Httpjail should correct the Host header to www.cloudflare.com, allowing the request (got: {})",
+        stdout.contains("\"Host\": \"httpbin.org\"") || stdout.contains("\"Host\":\"httpbin.org\""),
+        "Httpjail should correct Host header to httpbin.org (got: {})",
         stdout
     );
+
+    // Verify the mismatched header was NOT forwarded
     assert!(
-        !stdout.contains("error code: 1034"),
-        "Httpjail-corrected request should not be blocked by Cloudflare (got: {})",
+        !stdout.contains("\"Host\": \"evil.com\"") && !stdout.contains("\"Host\":\"evil.com\""),
+        "Httpjail should not forward mismatched Host header evil.com (got: {})",
         stdout
     );
 
-    // This demonstrates that httpjail prevents the Host header bypass attack
-    // that would otherwise be possible with direct curl execution
+    // This demonstrates that httpjail prevents Host header bypass attacks
+    // by correcting the Host header to match the actual destination URL
 }
 
 // The proc/JS parity tests have been moved to tests/json_parity.rs