This pull request serves as an optimization for batch requests that require authentication.

Expected Result:
If the batch endpoint requires authentication, it should re-use those credentials for any of the subsequent injected requests. In other words, it should only check the session storage once for all the requests in a batch.

Actual Result:
The subsequent requests ignore the initial credential validation and performs a session lookup for the n requests.

Reproduction Steps:

1. Apply an authentication strategy to your batch endpoint (e.g.)

    options: {
      batchEndpoint: '/api/batch',
      tags: ['batch'],
      auth: 'session'
    }

2. Define an endpoint that requires the same authentication strategy (e.g.)

  {
    method: 'POST',
    path: '/api/users',
    config: {
      auth: {
        strategy: 'session',
        scope: ['users:read']
      }
    },
    handler: UserController.createUser
  }

3. Make a POST request with a payload (e.g.)

[ { method: 'POST',
    path: '/api/users',
    payload: { first_name: 'Andrew', last_name: 'Fake' } },
  { method: 'POST',
    path: '/api/users',
    payload: { first_name: 'John', last_name: 'Doe' } } ]

4. Observe session storage. The session lookup is linear to the number requests instead of constant.