How to supply IdentityServer Key for deployment to production

If you install the dotnetcore3 SDK and create the dotnetcore/react project, it compiles and runs fine. Modifications to use external identity providers are straightforward and work as documented.

However, when I package the app using dotnet publish, and then run this release code, I get this error message (I have truncated the stack trace):

info: IdentityServer4.Startup[0]
      Starting IdentityServer4 version
crit: Microsoft.AspNetCore.Hosting.Diagnostics[6]
      Application startup exception
System.InvalidOperationException: Key type not specified.
   at Microsoft.AspNetCore.ApiAuthorization.IdentityServer.ConfigureSigningCredentials.LoadKey()
   at Microsoft.AspNetCore.ApiAuthorization.IdentityServer.ConfigureSigningCredentials.Configure(ApiAuthorizationOptions options)

So... it uses IdentityServer, and it wants some sort of key. At this point the documentation trail basically peters out.

Can someone guide me as to what it wants and how to provide it?

I mean this sort of thing:

Read [link to page] for the crypto algorithms you can use

If you choose [common option] then you need [some tool] available from [tool url]

After you generate the cert file (or whatever) put it [where it goes] in your project and add [sample config snip] to your [appropriate config file]

I found this on the IdentityServer documentation but it's too general

Possible duplicate

After posting I found this InvalidOperationException: Key type not specified. Microsoft.AspNetCore.ApiAuthorization.IdentityServer.ConfigureSigningCredentials.LoadKey()

It looks like it may be the same question fundamentally. If it turns out to be the same thing I will remove this myself.