Add the ability to create or update a Service Subscription using the 3scale API

Current Behaviour

A subset of the APIs (Services/products) are classified as hidden and the users which should gain access cannot be identified via builtin features such as groups, custom fields or otherwise. These users are provided access to this set of APIs on demand on a case by case basis. There is no way to fully automate the management of these users for an Admin of the hidden API(s) where it is required to perform the following actions:

• Subscribe the Developer user to the Service/Product via Service Plans.
• Approve the subscription.

Expected behaviour

A subset of the APIs (Services/products) are classified as hidden and the users which should gain access cannot be identified via builtin features such as groups, custom fields or otherwise. These users are provided access to this set of APIs on demand on a case by case basis. It should be therefore possible to fully automate the management of these users for an Admin of the hidden API(s) where it is required to perform the following actions:

• Subscribe the Developer user to the Service/Product via Service Plans.
• Approve the subscription.
  Ideally this functionality would be exposed via the Account Management API with the addition of the following 2 API endpoints:
• Service Subscription Accept API (currently this feature only exists in the UI)
• Service Subscription Update API (to facilitate any service plan updates/changes that can currently only be done in the UI)

Workaround

Use the Application Create API which should then create the service subscription (contract) in the background then accept/approve the subscription via the UI. Additionally to make any service plan updates/changes this also has to be performed via the UI in the "plan change" view.

Dev Notes: Please read all the comments.