Ok, so I have quite a few requests on what I would like to be able to do with the Rest API. Could you please consider extending it? It feels quite lacking: 

Extend existing endpoints to let us provide the following information

• POST core/members: Let us provide an IP address the member should be registered with
• POST core/members: Let us set whether account should be in a validated state
• GET core/members: Let us search for members by other fields, like displayname, email or any other database column on the core_members-table. We don't necessarily know the member ID. 
• POST core/members: We have an unique column on the core_members-table that corresponds to an ID in another user table. Let us provide such other values when creating and editing a member. This should also be searchable with GET core/members. 

 

New features

• Add/remove member to/from secondary group
• Get a member to follow items and containers (topics and forums)
• Validate a member

Alternatively, would it be possible for me to easily extend the API to add these things myself? How should I go about doing that? 

You can certain write plugins that extend the REST API, however I've also raised your requests internally for further consideration.