Security: Add input validation and improve logging safety documentation

[leogdion]

Overview

Address security considerations identified during PR #134 review, focusing on input validation and clear security documentation.

Issues to Address

1. Enhanced Logging Redaction Documentation

Location: MistKitLogger.swift

Current State: Environment variable MISTKIT_DISABLE_LOG_REDACTION exists but lacks prominent warnings.

Recommendation: Add explicit warnings in code documentation:

/// - Warning: Setting MISTKIT_DISABLE_LOG_REDACTION=1 will log sensitive data including
///   API tokens and user data. NEVER enable this in production environments.
internal static var isRedactionDisabled: Bool { ... }

Also add to README and migration guides with clear security warnings.

2. Field Name Input Validation

Location: Filter builders throughout codebase

Issue: Filter builders don't validate field names for potential injection attacks or special characters that could cause issues.

Recommendation: Add field name validation:

private static func validateFieldName(_ name: String) throws {
  guard name.allSatisfy({ $0.isLetter || $0.isNumber || $0 == "_" }) else {
    throw FilterError.invalidFieldName(name)
  }
}

Apply validation consistently across all filter building methods.

3. Security Best Practices Documentation

Action Items:

• Add security section to README
• Document safe logging practices
• Provide examples of secure filter construction
• Add security testing checklist

Benefits

• Prevent injection attacks
• Clear security expectations for users
• Protect sensitive data in logs
• Follow security best practices

Related

• PR Adding Celestra to Demos #134

Labels

security, documentation