You can get the file keys using the “GET project files” endpoint.

https://www.figma.com/developers/api#get-project-files-endpoint

Nice. How to get the project_id and team_id? Is any option for get automatically using REST API?

You can get the project IDs using the “GET team projects” endpoint.

https://www.figma.com/developers/api#get-team-projects-endpoint

And there is no endpoint for teams.

This is a security measure currently given that there are no fine-grained permissions in the REST API. You have to ask the user to give you the necessary links manually, and thus the user understands that you get the permission to the scope of the link you are asking from them. Otherwise every service provider using the REST API would have access to every single file of every single user they have, and that is not ideal, especially when you don’t need such broad scope of access (most often you just need a single file or two).