Out of curiosity (and self interest [1]), what is your use case for digital signing and verification?

My understanding is that it’s more about trust (Docusign being the leader) than anything else: one can provide certificate signing and verification, but the trust in the owner of the certificate is the crux of the matter

[1] I’m the developer behind SimplePDF.eu

I guess you could reverse proxy with nginx?

As you probably should?