Another option is to avoid using a self-signed SSL certificate. Instead, create a real, issued SSL certificate using something like Let's Encrypt (or similar free services)
My REST API is running under HTTPS, but some of its "link" URLs are switching to HTTP?
This scenario may occur when you are running the REST API behind an HTTP proxy (e.g. Apache HTTPD's
proxy_pass or any other proxy that is forwarding from HTTPS to HTTP).
The fix is to ensure the DSpace REST API is sent the
X-Forwarded-Proto header (by your proxying service), telling it that the forwarded protocol is HTTPS
In general, when running behind a proxy, the DSpace REST API depends on accurate X-Forwarded-* headers to be sent by that proxy.