fix(#1514): add client-side auth and security tests for WebSocket gateway

- Add client-side token authentication in app.js for external connections
- Skip auth for localhost (127.0.0.1, ::1, localhost)
- Token read from localStorage ('nexus-ws-auth-token')
- Add comprehensive security tests (tests/test_websocket_security.py)
- Tests verify server binding, env vars, and client auth implementation

Server-side fix already present on main via PR #1504:
- HOST defaults to 127.0.0.1
- AUTH_TOKEN support via server.py authenticate_connection()
- Rate limiting already implemented

Closes #1514

tests/test_websocket_security.py

@@ -0,0 +1,165 @@
+#!/usr/bin/env python3
+"""
+Test WebSocket gateway security configuration.
+Issue #1514: [Security] WebSocket gateway listens on 0.0.0.0
+"""
+
+import os
+import re
+import sys
+
+
+def test_server_binding():
+    """Test that server binds to correct address."""
+    print("Testing server binding configuration...")
+    
+    server_path = os.path.join(os.path.dirname(__file__), '..', 'server.py')
+    
+    if not os.path.exists(server_path):
+        print(f"ERROR: server.py not found at {server_path}")
+        return False
+    
+    with open(server_path, 'r') as f:
+        content = f.read()
+    
+    # Check HOST uses env var with 127.0.0.1 default (flexible whitespace)
+    host_pattern = r'HOST\s*=\s*os\.environ\.get\(\s*"NEXUS_WS_HOST"\s*,\s*"127\.0\.0\.1"\s*\)'
+    if re.search(host_pattern, content):
+        print("HOST configured with env var, default 127.0.0.1")
+    else:
+        print("HOST not properly configured")
+        return False
+    
+    # Check for authentication implementation
+    if 'async def authenticate_connection' in content:
+        print("Server-side authentication implemented")
+    else:
+        print("Server-side authentication missing")
+        return False
+    
+    # Check for token validation
+    if 'token' in content and 'AUTH_TOKEN' in content:
+        print("Token validation present")
+    else:
+        print("Token validation missing")
+        return False
+    
+    return True
+
+
+def test_environment_variables():
+    """Test environment variable configuration."""
+    print("\nTesting environment variable configuration...")
+    
+    server_path = os.path.join(os.path.dirname(__file__), '..', 'server.py')
+    
+    with open(server_path, 'r') as f:
+        content = f.read()
+    
+    checks = [
+        ('NEXUS_WS_HOST', "HOST environment variable"),
+        ('NEXUS_WS_PORT', "PORT environment variable"),
+        ('NEXUS_WS_TOKEN', "Auth token environment variable"),
+    ]
+    
+    for var, desc in checks:
+        if f'NEXUS_WS_{var.split("_")[-1]}' in content or var in content:
+            # More precise check
+            if f'os.environ.get("{var}"' in content or f"os.environ.get('{var}'" in content:
+                print(f"{desc} configured")
+            else:
+                print(f"{desc} not found via os.environ.get")
+                return False
+        else:
+            print(f"{desc} missing")
+            return False
+    
+    # Check 127.0.0.1 default
+    host_pattern = r'HOST\s*=\s*os\.environ\.get\(\s*"NEXUS_WS_HOST"\s*,\s*"127\.0\.0\.1"'
+    if re.search(host_pattern, content):
+        print("Default HOST is 127.0.0.1")
+    else:
+        print("Default HOST is not 127.0.0.1")
+        return False
+    
+    return True
+
+
+def test_client_authentication():
+    """Test client authentication code."""
+    print("\nTesting client authentication code...")
+    
+    app_path = os.path.join(os.path.dirname(__file__), '..', 'app.js')
+    
+    if not os.path.exists(app_path):
+        print(f"ERROR: app.js not found at {app_path}")
+        return False
+    
+    with open(app_path, 'r') as f:
+        content = f.read()
+    
+    checks = [
+        ('isLocalhost', 'Client checks for localhost'),
+        ('nexus-ws-auth-token', 'Client retrieves auth token'),
+        ("type: 'auth'", 'Client sends auth message'),
+        ('localStorage.getItem', 'Client reads from localStorage'),
+    ]
+    
+    for pattern, desc in checks:
+        if pattern in content:
+            print(desc)
+        else:
+            print(f"MISSING: {desc}")
+            return False
+    
+    return True
+
+
+def main():
+    """Run all tests."""
+    print("=" * 60)
+    print("WebSocket Gateway Security Tests")
+    print("Issue: #1514")
+    print("=" * 60)
+    
+    tests = [
+        ("Server binding configuration", test_server_binding),
+        ("Environment variable configuration", test_environment_variables),
+        ("Client authentication code", test_client_authentication),
+    ]
+    
+    results = []
+    for name, test_func in tests:
+        print(f"\n{name}:")
+        try:
+            result = test_func()
+            results.append((name, result))
+        except Exception as e:
+            print(f"Test failed with exception: {e}")
+            import traceback
+            traceback.print_exc()
+            results.append((name, False))
+    
+    print("\n" + "=" * 60)
+    print("Test Results")
+    print("=" * 60)
+    
+    passed = 0
+    for name, result in results:
+        status = "PASS" if result else "FAIL"
+        print(f"  {status}: {name}")
+        if result:
+            passed += 1
+    
+    print(f"\nPassed: {passed}/{len(results)}")
+    
+    if passed == len(results):
+        print("\nAll tests passed!")
+        return 0
+    else:
+        print("\nSome tests failed!")
+        return 1
+
+
+if __name__ == '__main__':
+    sys.exit(main())