uploading content to sub-domain from main domain

I have a custom CMS built using laravel, I want to modify its functionality and move static content to a subdomain. I want to add a form in my main domain i.e. example.com to upload the content however the content should be uploaded to a subdomain i.e. static.example.com which is on a different server. what is the right way to approach this problem? I am thinking about creating an API on the subdomain that accepts file uploads and calls this from the main domain while submitting the form from the main domain server. I am not aware of the proper way to call that API and secure the API on subdomain. Any suggestion or right direction will be appreciated.