Redirect and transfer part of URL

Support
1

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 example.com. The URL endpoint generated by firebase functions is:
https://us-central1-firebaseproj.cloudfunctions.net/apiRoutes

Behind that endpoint is an express instance that can handle multiple routes e.g.:
/year/2021/month/02/day/1

So the combined URL is: https://us-central1-firebaseproj.cloudfunctions.net/apiRoutes/year/2021/month/02/day/1

How would I write the redirect so the information about year, month and day is transferred to the redirect granted the link was:
example.com/year/2021/month/02/day/1

Tl:DR I want to redirect:
http://example.com/year/2021/month/02/day/1 to
https://us-central1-firebaseproj.cloudfunctions.net/apiRoutes/year/2021/month/02/day/1
but the year, month and day is user defined and therefore dynamic

2

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

http://example.com/year/:year/month/:month/day/day https://us-central1-firebaseproj.cloudfunctions.net/apiRoutes/year/:year/month/:month/day/day 301!