Improve OAuth/OpenID Connect token validation performance

## Description

Currently, the OAuth/OpenID Connect token validation process in the Janssen Auth Server could be optimized for better performance, especially when handling high-volume authentication requests.

## Problem Statement

When multiple clients make concurrent token validation requests, we observe:
- Increased response times
- Higher CPU utilization
- Potential bottlenecks in the token validation pipeline

## Proposed Solution

1. Implement token validation caching with appropriate TTL
2. Optimize cryptographic operations for signature verification
3. Add connection pooling for backend services
4. Implement concurrent request handling improvements

## Expected Benefits

- Reduced latency in token validation responses
- Better throughput for concurrent requests
- Improved overall system performance
- Enhanced scalability for enterprise deployments

## Additional Context

This improvement will help organizations running Janssen with high authentication volumes to achieve better performance metrics and user experience.

Labels: performance, oauth, openid-connect, enhancement

Start by examining the Janssen Auth Server token validation process and measuring its behavior under concurrent, high-volume authentication requests. Evaluate the proposed caching, cryptographic-operation, backend-connection, and concurrency areas; the work is done when latency, CPU utilization, throughput, and scalability improve without weakening token validation.

Written by the indexing model from the issue text.