Critical Security Vulnerabilities in SDK Credential Management

## Overview
This issue documents critical security vulnerabilities identified in the Bedrock AgentCore SDK related to credential management, endpoint validation, and token handling.

## Vulnerabilities Identified
- **Endpoint Validation**: Hardcoded endpoints without proper validation allow potential injection attacks
- **Token Management**: Lack of proper token lifecycle management leading to potential token leaks
- **Input Validation**: Missing validation for user inputs creating security risks
- **Credential Exposure**: Sensitive credentials potentially exposed in log files

## Impact
These vulnerabilities could lead to:
- Unauthorized access to AWS resources
- Credential leakage
- Potential injection attacks
- Non-compliance with AWS security best practices

## Resolution
A comprehensive security framework has been implemented in PR #16 that addresses all identified vulnerabilities with:

- AWS domain pattern validation
- Thread-safe token lifecycle management
- Input sanitization and validation
- Secure logging practices

## Related PR
This issue is being addressed in PR #16: Security & Credential Management Enhancements

Commencez par PR #16, que l’issue identifie comme implémentant la résolution, et examinez ses changements au regard des quatre vulnérabilités listées. Confirmez que la validation des endpoints, le cycle de vie des tokens, la validation des entrées et la journalisation sécurisée sont couverts ; l’issue ne fournit ni fichiers ni tests pour un travail indépendant.

Rédigé par le modèle d'indexation à partir du texte de l'issue.