Ask HN: How do you build a developer dashboard?

I know this sounds dumb, but honestly, once I have a fully working API and stuff, how do I actually build a developer dashboard.

By dashboard I mean like the web interface where developers can sign in, manage applications, permissions, authorizations, generate secret keys etc.

Most of the APIs I use have this online, but I don't where to start when building one for my own API. Is there a company, SaaS that offers such or everything has to be written from scratch?

Any help would be greatly appreciated.