Problem description
The SubscriptionDetail schema used in the subscription APIs currently makes device a mandatory parameter:

    SubscriptionDetail:
      description: The detail of the requested event subscription
      type: object
      properties:
        device:
          $ref: '#/components/schemas/Device'
      required:
        - device

But if the subscription is created using a 3-legged token, then no device parameter should be provided.

Expected behaviour
device should be an optional parameter in SubscriptionDetail

    SubscriptionDetail:
      description: The detail of the requested event subscription
      type: object
      properties:
        device:
          $ref: '#/components/schemas/Device'

Alternative solution
subscriptionDetail itself could also be made optional in the Config schema. But this might cause issues if additional parameters were later added to SubscriptionDetail

Additional context