Redirect and transfer part of URL

I’ve built an API using firebase cloud functions and I want to set up redirects on Netlify to redirect to those http functions so I can use my domain to keep branding consistent.

Let’s say my project on firebase is firebaseproj and my domain on Netlify is The URL endpoint generated by firebase functions is:

Behind that endpoint is an express instance that can handle multiple routes e.g.:

So the combined URL is:

How would I write the redirect so the information about year, month and day is transferred to the redirect granted the link was:

Tl:DR I want to redirect: to
but the year, month and day is user defined and therefore dynamic

Using a placeholder is exactly what was required. In _redirects: 301!