A custom identity context to intercept user adds

ApplicationCosmosDbContext.cs

using BlazorCosmosWasm.Server.Controllers;
using BlazorCosmosWasm.Server.Models;
using BlazorCosmosWasm.Shared;
using IdentityServer4.EntityFramework.Options;
using Microsoft.Azure.Cosmos;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Options;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace BlazorCosmosWasm.Server.Data
{
    public class ApplicationCosmosDbContext : ApplicationDbContext
    {
        private readonly IConfiguration _config;
        private CosmosClient client;

        private CosmosClient Get_client()
        {
            if (client == null)
            {
                client = _config.CreateCosmosClientFromConfig();
            }
            return client;
        }

        public ApplicationCosmosDbContext(IConfiguration config, DbContextOptions options, IOptions<OperationalStoreOptions> operationalStoreOptions) : base(options, operationalStoreOptions)
        {
            _config = config;
        }

        public override async Task<int> SaveChangesAsync(CancellationToken cancellationToken = new CancellationToken())
        {
            var newUsers = ChangeTracker.Entries<ApplicationUser>().Where(u => u.State == EntityState.Added);

            foreach(var newUser in newUsers)
            {
                await AddToCosmosAsync(newUser.Entity.Email);
            }

            var result = await base.SaveChangesAsync(cancellationToken);

            return result;
        }

        private async Task AddToCosmosAsync(string email)
        {
            var db = Get_client().GetDatabase(BlogContext.DatabaseName);
            await db.CreateUserAsync(email);
            Debug.WriteLine($"Added {email} to Cosmos.");
        }
    }
}