asp.net core 自定义 Policy 替换 AllowAnonymous 的行为

Intro

最近对我们的服务进行了改造，原本内部服务在内部可以匿名调用，现在增加了限制，通过 identity server 来管理 api 和 client，网关和需要访问api的客户端或api服务相互调用通过 client_credencial 的方式来调用，这样一来我们可以清晰知道哪些 api 服务会被哪些 api/client 所调用，而且安全性来说更好。为了保持后端服务的代码更好的兼容性，希望能够实现相同的代码通过在 Startup 里不同的配置实现不同的 Authorization 逻辑，原来我们的服务的 Authorize 都是以 Authorize("policyName") 的形式来写的，这样一来我们只需要修改这个 Policy 的授权配置就可以了。对于 AllowAnonymous 就希望可以通过一种类似的方式来实现，通过自定义一个 Policy 来实现自己的逻辑

实现方式

将 action 上的 AllowAnonymous 替换为 Authorize("policyName")，在没有设置 Authorize 的 controller 上增加 Authorize("policyName")

public class AllowAnonymousPolicyTransformer : IApplicationModelConvention
{
 private readonly string _policyName;
 public AllowAnonymousPolicyTransformer() : this("anonymous")
 {
 }
 public AllowAnonymousPolicyTransformer(string policyName) => _policyName = policyName;
 public void Apply(ApplicationModel application)
 {
 foreach (var controllerModel in application.Controllers)
 {
 if (controllerModel.Filters.Any(_ => _.GetType() == typeof(AuthorizeFilter)))
 {
 foreach (var actionModel in controllerModel.Actions)
 {
 if (actionModel.Filters.Any(_ => _.GetType() == typeof(AllowAnonymousFilter)))
 {
 var allowAnonymousFilter = actionModel.Filters.First(_ => _.GetType() == typeof(AllowAnonymousFilter));
 actionModel.Filters.Remove(allowAnonymousFilter);
 actionModel.Filters.Add(new AuthorizeFilter(_policyName));
 }
 }
 }
 else
 {
 if (controllerModel.Filters.Any(_ => _.GetType() == typeof(AllowAnonymousFilter)))
 {
 var allowAnonymousFilter = controllerModel.Filters.First(_ => _.GetType() == typeof(AllowAnonymousFilter));
 controllerModel.Filters.Remove(allowAnonymousFilter);
 }
 controllerModel.Filters.Add(new AuthorizeFilter(_policyName));
 }
 }
 }
}
public static class MvcBuilderExtensions
{
 public static IMvcBuilder AddAnonymousPolicyTransformer(this IMvcBuilder builder)
 {
 builder.Services.Configure<MvcOptions>(options =>
 {
 options.Conventions.Insert(0, new AllowAnonymousPolicyTransformer());
 });
 return builder;
 }
 public static IMvcBuilder AddAnonymousPolicyTransformer(this IMvcBuilder builder, string policyName)
 {
 builder.Services.Configure<MvcOptions>(options =>
 {
 options.Conventions.Insert(0, new AllowAnonymousPolicyTransformer(policyName));
 });
 return builder;
 }
}

controller 中的代码：

[Route("api/[controller]")]
public class ValuesController : Controller
{
 private readonly ILogger _logger;
 public ValuesController(ILogger<ValuesController> logger)
 {
 _logger = logger;
 }
 // GET api/values
 [HttpGet]
 public ActionResult<IEnumerable<string>> Get()
 {
 var msg = $"IsAuthenticated: {User.Identity.IsAuthenticated} ,UserName: {User.Identity.Name}";
 _logger.LogInformation(msg);
 return new string[] { msg };
 }
 // GET api/values/5
 [Authorize]
 [HttpGet("{id:int}")]
 public ActionResult<string> Get(int id)
 {
 return "value";
 }
 // ...
}

Startup 中 ConfigureServices 配置：

var anonymousPolicyName = "anonymous";
services.AddAuthorization(options =>
{
 options.AddPolicy(anonymousPolicyName, builder => builder.RequireAssertion(context => context.User.Identity.IsAuthenticated));
 options.DefaultPolicy = new AuthorizationPolicyBuilder(HeaderAuthenticationDefaults.AuthenticationSchema)
 .RequireAuthenticatedUser()
 .RequireAssertion(context => context.User.GetUserId<int>() > 0)
 .Build();
});
services.AddMvc(options =>
 {
 options.Conventions.Add(new ApiControllerVersionConvention());
 })
 .AddAnonymousPolicyTransformer(anonymousPolicyName)
 ;