要给出“ASP.NET Core - 动态策略授权”的代码示例，您可以按照以下步骤进行操作：

1. 创建一个新的ASP.NET Core Web应用程序项目。
2. 在 Startup.cs 文件中添加以下代码：

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;

namespace DynamicPolicyAuthorization
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();

            services.AddAuthorization(options =>
            {
                options.AddPolicy("DynamicPolicy", policy =>
                {
                    policy.Requirements.Add(new DynamicAuthorizationRequirement());
                });
            });

            services.AddSingleton();
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.UseRouting();

            app.UseAuthentication();
            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }
}

3. 创建一个名为 DynamicAuthorizationRequirement.cs 的新类文件，并添加以下代码：

using Microsoft.AspNetCore.Authorization;

namespace DynamicPolicyAuthorization
{
    public class DynamicAuthorizationRequirement : IAuthorizationRequirement
    {
        public string Role { get; set; }

        public DynamicAuthorizationRequirement(string role)
        {
            Role = role;
        }
    }
}

4. 创建一个名为 DynamicAuthorizationHandler.cs 的新类文件，并添加以下代码：

using Microsoft.AspNetCore.Authorization;
using System.Security.Claims;
using System.Threading.Tasks;

namespace DynamicPolicyAuthorization
{
    public class DynamicAuthorizationHandler : AuthorizationHandler
    {
        protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, DynamicAuthorizationRequirement requirement)
        {
            if (context.User.HasClaim(ClaimTypes.Role, requirement.Role))
            {
                context.Succeed(requirement);
            }

            return Task.CompletedTask;
        }
    }
}

5. 创建一个名为 ValuesController.cs 的新控制器文件，并添加以下代码：

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

namespace DynamicPolicyAuthorization.Controllers
{
    [ApiController]
    [Authorize(Policy = "DynamicPolicy")]
    [Route("api/[controller]")]
    public class ValuesController : ControllerBase
    {
        [HttpGet]
        public ActionResult Get()
        {
            return "Authorized";
        }
    }
}

6. 运行应用程序，并尝试访问 /api/values 路由。只有当用户具有相应角色时，才能访问该路由。

这是一个基本示例，演示了如何在ASP.NET Core中使用动态策略授权。您可以根据需要进行修改和扩展。