要自定义ASP .NET Core Identity的ApiAuthorizationDbContext，您可以按照以下步骤操作：

1. 创建一个新的类，继承自ApiAuthorizationDbContext。这个类将用于自定义Identity的数据库上下文。

using Microsoft.AspNetCore.ApiAuthorization.IdentityServer;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using IdentityServer4.EntityFramework.Options;

public class CustomApiAuthorizationDbContext : ApiAuthorizationDbContext
{
    public CustomApiAuthorizationDbContext(
        DbContextOptions options,
        IOptions operationalStoreOptions) : base(options, operationalStoreOptions)
    {
    }
}

2. 在Startup.cs文件中，将默认的ApiAuthorizationDbContext替换为自定义的CustomApiAuthorizationDbContext。

using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

public class Startup
{
    private readonly IConfiguration _configuration;

    public Startup(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext(options =>
            options.UseSqlServer(_configuration.GetConnectionString("DefaultConnection")));

        services.AddDefaultIdentity()
            .AddEntityFrameworkStores();

        services.AddIdentityServer()
            .AddApiAuthorization();

        // 其他服务配置

        services.AddControllersWithViews();
        services.AddRazorPages();
    }

    // 其他配置方法
}

3. 确保您在appsettings.json文件或其他配置文件中定义了数据库连接字符串。

{
  "ConnectionStrings": {
    "DefaultConnection": "YourConnectionStringHere"
  }
}

通过以上步骤，您将能够自定义ASP .NET Core Identity的ApiAuthorizationDbContext，并在应用程序中使用它。