Supplying Azure SQL DB connection string for ASP.NET Core MVC & EF Core solution

Question

I believe I am following Microsoft recommended methodology and that I have the components required but can't figure out how to pull it together.

My am using Azure App Configuration service to store a key vault key (along with other configuration settings) and the Key Vault service to supply a database connection string that contains Azure SQL Server username/password)

I have separate working project/solutions (ASP.NET Core MVC) for the following:

• A working Azure web app with Azure SQL DB functionality that outputs CRUD & table data
• A working Azure web app that outputs a string 'secret' using Azure App Configuration for the key & Key Vault for the secret
• I have used Managed ID to access all Azure resources

Using a test app I can output the dummy configuration data from my Azure App Configuration & Key Vault services using code from 3 project files:

• Program.cs webBuilder.ConfigureAppConfiguration((context, config)
• appsettings.json "AzureAppConfigurationEndpoint": "https://xxxxxxxxxx.azconfig.io"
• /Views/~/razor page @Configuration["TestApp:Settings:KeyVaultDbString"]

My db app accesses the db connection string using code in these files:

• Startup.cs public void ConfigureServices(IServiceCollection services)
• appsettings.json"DefaultConnection":"Server=tcp:xxxx.database.windows.net,1433;XXXXXXX"

I want to upgrade my db app to use the connection string configuration value supplied by the test app. Therefore the plan is:

Incorporate code from test app Program.cs into db app Program.cs. I don't see a problem with this.

public static IHostBuilder CreateHostBuilder(string[] args) =>
 Host.CreateDefaultBuilder(args)
     .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.ConfigureAppConfiguration((context, config) =>
            {
                var settings = config.Build();
                var appConfigurationEndpoint = settings["AzureAppConfigurationEndpoint"];

                config.AddAzureAppConfiguration(options =>
                   {
                       options.Connect(new Uri(appConfigurationEndpoint), new DefaultAzureCredential());

                           options.ConfigureKeyVault(kv =>
                            {
                                kv.SetCredential(new DefaultAzureCredential());
                            });
                   });

                webBuilder.UseStartup<Startup>();
            });
        });

But. At this point I don't know how to access the ["TestApp:Settings:KeyVaultDbString"] configuration data in Startup.cs. To supply the "KeyVaultDbString" as a substitute for my "DefaultConnection".

This is the existing code:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection")));
    services.AddDatabaseDeveloperPageExceptionFilter();

    services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
            .AddEntityFrameworkStores<ApplicationDbContext>();
    services.AddControllersWithViews();

    // this code is responsible for login-intercept required for solution
    services.AddAuthorization(options =>
        {
            options.FallbackPolicy = new AuthorizationPolicyBuilder()
                .RequireAuthenticatedUser()
                .Build();
        });
}

While accessing the Azure configuration data from a view page is easy using @Configuration["TestApp:Settings:KeyVaultMessage"] How do I access when I configure services in my Startup.cs?

I have read Configuration in ASP.NET Core. I understand the following:

• Azure App Configuration & Key Vault are configuration providers (like appsettings, environment variables & those supplied on the command line)
• The section under 'Connection string prefixes' is relevant but there are no code examples
• The section under Custom configuration provider details options building which may be required for my situation
• The sections under 'Access configuration in Startup' & 'Access configuration in Razor Pages' seems to relate directly to the syntax I am using. But still leaves me wondering how to separate my string from it's label for using as "DefaultConnection" for my db app.

Any suggestions would be appreciated.