REST API Authentication method: custom header

Hey team,
When creating a REST API resource, I can set custom headers. That's all joyful.
However, one of the APIs I need to connect to uses a custom X-Access-Token header, and if I input this on the resource, the access token is exposed in the client and isn't encrypted.
That's not ideal.

Would love if I under "Authentication" could select "Custom Headers" and set it up there :-).