Razor Pages - multiple routes for same page

In my ASP.NET Razor Pages project I have for my Post entity an Edit page in the Pages folder named PostEdit.cshtml.

I want to get to it using the URL "/posts/edit/{id?}", so I have at the top of the page:

@page "/posts/edit/{id?}"

To avoid code duplication, I want to use the same page also for adding a new Post, having a different route presented to the user, "/posts/add".

But I cannot add multiple routes to a single Razor page, adding a second @page directive gives an error.

After a lot of googling and trying different things I was able to use a feature that seems to be named Friendly Routes, using AddPageRoute from Conventions when setting up the Razor Pages in the Startup.cs or the Program.cs file.

services.AddRazorPages(options =>
{
    options.Conventions.AddPageRoute("/PostEdit", "/posts/add");
});