Hi,
- secure access to your api with JWT
- Use tokens/slugs instead of real id's so no one can figure out numbering on your models and therefore figure out how it it structured.
- Generate separate encryption key per every client and use it to pass ecrypted data between him and your server.
It has also been asked before:
https://laracasts.com/discuss/channels/lumen/how-to-encrypt-the-response-from-an-api
Hope it helps!