Description of problem:  **

Getting 500 on APIs (/api/permission/plugins/policies and /api/permission/plugins/condition-rules)if there is typo/wrong entry for below config

permission:
   enabled: true
   rbac:
     policies-csv-file: /Users/jakumar/Workspaces/backstage-plugins/rbac-policy.csv
     pluginsWithPermission:
       - catalog
       - permission
       - scaffolder
       - kubernetes34

error can be seen below

{
    "error": {
        "name": "Error",
        "message": "Unable to generate legacy token for communication with the 'kubernetes34' plugin. You will typically encounter this error when attempting to call a plugin that does not exist, or is deployed with an old version of Backstage; caused by Error: Unable to generate legacy token, no legacy keys are configured in 'backend.auth.keys' or 'backend.auth.externalAccess'",
        "cause":

{             "name": "Error",             "message": "Unable to generate legacy token, no legacy keys are configured in 'backend.auth.keys' or 'backend.auth.externalAccess'",             "stack": "Error: Unable to generate legacy token, no legacy keys are configured in 'backend.auth.keys' or 'backend.auth.externalAccess'\n    at DisabledTokenManager.getToken (/Users/jakumar/Workspaces/backstage-plugins/node_modules/@backstage/backend-common/src/tokens/ServerTokenManager.ts:48:11)\n    at DefaultAuthService.getPluginRequestToken (/Users/jakumar/Workspaces/backstage-plugins/node_modules/@backstage/backend-app-api/src/services/implementations/auth/DefaultAuthService.ts:154:34)\n    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n    at PluginPermissionMetadataCollector.getPluginMetaData (/Users/jakumar/Workspaces/backstage-plugins/plugins/rbac-backend/src/service/plugin-endpoints.ts:101:25)\n    at PluginPermissionMetadataCollector.getPluginPolicies (/Users/jakumar/Workspaces/backstage-plugins/plugins/rbac-backend/src/service/plugin-endpoints.ts:77:28)\n    at <anonymous> (/Users/jakumar/Workspaces/backstage-plugins/plugins/rbac-backend/src/service/policies-rest-api.ts:767:20)"         }

,
        "stack": "Error: Unable to generate legacy token for communication with the 'kubernetes34' plugin. You will typically encounter this error when attempting to call a plugin that does not exist, or is deployed with an old version of Backstage; caused by Error: Unable to generate legacy token, no legacy keys are configured in 'backend.auth.keys' or 'backend.auth.externalAccess'\n    at <anonymous> (/Users/jakumar/Workspaces/backstage-plugins/node_modules/@backstage/backend-app-api/src/services/implementations/auth/DefaultAuthService.ts:155:17)\n    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)"
    },
    "request":

{         "method": "GET",         "url": "/api/permission/plugins/policies"     }

,
    "response":

{         "statusCode": 500     }

}

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Configure RBAC fronted / backend plugin
2. Add config as suggested above
3. try the endpoint using CURL or UI

Actual results:

API return 500 with above error

Expected results:

The data should be returned for the valid plugin / or for those permission policies exist should be shown

Reproducibility (Always/Intermittent/Only Once): Always

Build Details:

Additional info (Such as Logs, Screenshots, etc):