Initializing a DBConext with a different connection string on a per user basis in .Net Core

Question

I need to be able create a DBContext with a specific DB connection string depending on the logged in user.

Users login via a JWT token at which point the application makes a call to a 3rd party to determine which database they should be connected to.

I am currently registering my ApplicationDBContext at startup:

services.AddDbContextFactory<ApplicationDBContext>(options => options.UseSqlServer(
                    Configuration.GetConnectionString("TestDbConString"),
                    h => h.UseHierarchyId()
                ));

I also have this service:

services.
...
.onAuthenticated(async c => {

    await getConnectionData(); // Returns the connection string. This can take a few seconds the first time subsequently it returns cached data.

})

Obviously I need to change things up a bit. How would you go about registering ApplicationDBContext with the correct/custom connection string?

UPDATE:

Here is my poor attempt at setting up a DbContextFactory.

using Microsoft.EntityFrameworkCore;
using MyApp.Models;

namespace MyApp.Data
{

    public class ApplicationDbContextFactory : IDbContextFactory<AppDbContext>
    {


        public ApplicationDbContextFactory test(){
            return new ApplicationDbContextFactory();
        }

        public AppDbContext CreateDbContext()
        {

            string ConnectionString = "";


            //Magic here to get my ConnectionString.

            DbContextOptionsBuilder<AppDbContext> options = new DbContextOptionsBuilder<AppDbContext>();
            options.UseSqlServer(
                ConnectionString,
                h => h.UseHierarchyId()
            );

            return new AppDbContext(options.Options);
        }
    }
}

Startup,cs

                services.AddTransient<ApplicationDbContextFactory>();
                services.AddTransient(provider => provider.GetService<ApplicationDbContextFactory>()!.CreateDbContext());

I am now getting an error:

Unexpected Execution Error : No service for type 'Microsoft.EntityFrameworkCore.IDbContextFactory`1[MyApp.Data.AppDbContext]' has been registered.

Update #2 This fixed it:

Startup.cs

services.AddTransient<IDbContextFactory<AppDbContext>, ApplicationDbContextFactory>();