fix: remove hardcoded credentials and add security documentation

- Remove hardcoded API key and URL from debug-n8n-auth.ts
- Require environment variables with proper validation
- Add comprehensive SECURITY.md with best practices
- Address security concerns raised in issue #18

The SecureKeyGuard alert was a false positive (mistaking "validate_workflow"
for "VAULT_TOKEN"), but the review uncovered actual hardcoded credentials
that have now been removed.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

SECURITY.md

@@ -0,0 +1,95 @@
+# Security Policy
+
+## Reporting Security Vulnerabilities
+
+If you discover a security vulnerability in n8n-mcp, please report it by creating a private security advisory on GitHub or emailing the maintainer directly. Please do not create public issues for security vulnerabilities.
+
+## Security Best Practices
+
+### 1. Environment Variables
+
+**NEVER** commit real API keys, tokens, or credentials to the repository.
+
+- Use `.env` files for local development (already in `.gitignore`)
+- Use `.env.example` as a template with placeholder values
+- Generate strong tokens using: `openssl rand -base64 32`
+
+### 2. API Keys and Tokens
+
+- **Rotate credentials immediately** if they are exposed
+- Use environment variables exclusively - no hardcoded fallbacks
+- Implement proper token expiration when possible
+- Use least-privilege access for API keys
+
+### 3. Code Security
+
+#### ❌ DON'T DO THIS:
+```typescript
+// NEVER hardcode credentials
+const apiKey = process.env.N8N_API_KEY || 'n8n_api_actual_key_here';
+const apiUrl = process.env.N8N_API_URL || 'https://production-url.com';
+```
+
+#### ✅ DO THIS INSTEAD:
+```typescript
+// Always require environment variables
+const apiKey = process.env.N8N_API_KEY;
+const apiUrl = process.env.N8N_API_URL;
+
+if (!apiKey || !apiUrl) {
+  console.error('Error: Required environment variables are missing');
+  process.exit(1);
+}
+```
+
+### 4. Git Security
+
+Before committing, always check:
+```bash
+# Check for tracked sensitive files
+git ls-files | grep -E "\.(env|pem|key|cert)$"
+
+# Check staged changes for secrets
+git diff --staged | grep -iE "(api[_-]?key|secret|token|password)"
+```
+
+### 5. Docker Security
+
+- Never include `.env` files in Docker images
+- Use build arguments for compile-time configuration
+- Use runtime environment variables for secrets
+- Run containers as non-root users
+
+### 6. Dependencies
+
+- Regularly update dependencies: `npm audit`
+- Review dependency changes carefully
+- Use lock files (`package-lock.json`)
+- Monitor for security advisories
+
+## Security Checklist
+
+Before each release or deployment:
+
+- [ ] No hardcoded credentials in source code
+- [ ] All sensitive configuration uses environment variables
+- [ ] `.env` files are not tracked in git
+- [ ] Dependencies are up to date
+- [ ] No sensitive data in logs
+- [ ] API endpoints use proper authentication
+- [ ] Docker images don't contain secrets
+
+## Known Security Considerations
+
+1. **MCP Authentication**: When running in HTTP mode, always use strong `AUTH_TOKEN` values
+2. **n8n API Access**: The n8n API key provides full access to workflows - protect it carefully
+3. **Database Access**: The SQLite database contains node information but no credentials
+
+## Tools for Security
+
+- **SecureKeyGuard**: Automated scanning for exposed secrets
+- **npm audit**: Check for vulnerable dependencies
+- **git-secrets**: Prevent committing secrets to git
+- **dotenv-vault**: Secure environment variable management
+
+Remember: Security is everyone's responsibility. When in doubt, ask for a security review.

src/scripts/debug-n8n-auth.ts

@@ -7,8 +7,14 @@ import { config } from 'dotenv';
 config();
 
 async function debugN8nAuth() {
-  const apiUrl = process.env.N8N_API_URL || 'https://n8n.energyhouse.com.pl';
+  const apiUrl = process.env.N8N_API_URL;
-  const apiKey = process.env.N8N_API_KEY || 'n8n_api_f94c0b3fb3bf1a3a690f37bb0c5c0de43c7b690c0a33c88b6baaa37ae896dc96';
+  const apiKey = process.env.N8N_API_KEY;
+  
+  if (!apiUrl || !apiKey) {
+    console.error('Error: N8N_API_URL and N8N_API_KEY environment variables are required');
+    console.error('Please set them in your .env file or environment');
+    process.exit(1);
+  }
   
   console.log('Testing n8n API Authentication...');
   console.log('API URL:', apiUrl);