ASP.NET Core MVC 授权的扩展：自定义 Authorize Attribute 和 IApplicationModelProvide

一、概述

ASP.NET Core MVC 提供了基于角色( Role )、声明( Chaim ) 和策略 ( Policy ) 等的授权方式。在实际应用中，可能采用部门（ Department , 本文采用用户组 Group ）、职位 ( 可继续沿用 Role )、权限( Permission )的方式进行授权。要达到这个目的，仅仅通过自定义 IAuthorizationPolicyProvider 是不行的。本文通过自定义 IApplicationModelProvide 进行扩展。

二、PermissionAuthorizeAttribute : IPermissionAuthorizeData

AuthorizeAttribute 类实现了 IAuthorizeData 接口：

namespace Microsoft.AspNetCore.Authorization
{
  /// <summary>
  /// Defines the set of data required to apply authorization rules to a resource.
  /// </summary>
  public interface IAuthorizeData
  {
   /// <summary>
   /// Gets or sets the policy name that determines access to the resource.
   /// </summary>
   string Policy { get; set; }
   /// <summary>
   /// Gets or sets a comma delimited list of roles that are allowed to access the resource.
   /// </summary>
   string Roles { get; set; }
   /// <summary>
   /// Gets or sets a comma delimited list of schemes from which user information is constructed.
   /// </summary>
   string AuthenticationSchemes { get; set; }
  }
}

使用 AuthorizeAttribute 不外乎如下几种形式：

[Authorize]
[Authorize("SomePolicy")]
[Authorize(Roles = "角色1,角色2")]
[Authorize(AuthenticationSchemes = JwtBearerDefaults.AuthenticationScheme)]

当然，参数还可以组合起来。另外，Roles 和 AuthenticationSchemes 的值以半角逗号分隔，是 Or 的关系；多个 Authorize 是 And 的关系；Policy 、Roles 和 AuthenticationSchemes 如果同时使用，也是 And 的关系。

如果要扩展 AuthorizeAttribute，先扩展 IAuthorizeData 增加新的属性：

public interface IPermissionAuthorizeData : IAuthorizeData
{
    string Groups { get; set; }
    string Permissions { get; set; }
}

然后定义 AuthorizeAttribute:

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
public class PermissionAuthorizeAttribute : Attribute, IPermissionAuthorizeData
{
    public string Policy { get; set; }
    public string Roles { get; set; }
    public string AuthenticationSchemes { get; set; }
    public string Groups { get; set; }
    public string Permissions { get; set; }
}

现在，在 Controller 或 Action 上就可以这样使用了：

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[PermissionAuthorize(Roles = "经理,副经理")] // 经理或部门经理
[PermissionAuthorize(Groups = "研发部,生产部", Roles = "经理"] // 研发部经理或生成部经理。Groups 和 Roles 是 `And` 的关系。
[PermissionAuthorize(Groups = "研发部,生产部", Roles = "经理", Permissions = "请假审批"] // 研发部经理或生成部经理，并且有请假审批的权限。Groups 、Roles 和 Permission 是 `And` 的关系。

数据已经准备好，下一步就是怎么提取出来。通过扩展 AuthorizationApplicationModelProvider 来实现。

三、PermissionAuthorizationApplicationModelProvider : IApplicationModelProvider

AuthorizationApplicationModelProvider 类的作用是构造 AuthorizeFilter 对象放入 ControllerModel 或 ActionModel 的 Filters 属性中。具体过程是先提取 Controller 和 Action 实现了 IAuthorizeData 接口的 Attribute，如果使用的是默认的DefaultAuthorizationPolicyProvider，则会先创建一个 AuthorizationPolicy 对象作为 AuthorizeFilter 构造函数的参数。
创建 AuthorizationPolicy 对象是由 AuthorizationPolicy 的静态方法 public static async Task<AuthorizationPolicy> CombineAsync(IAuthorizationPolicyProvider policyProvider, IEnumerable<IAuthorizeData> authorizeData) 来完成的。该静态方法会解析 IAuthorizeData 的数据，但不懂解析 IPermissionAuthorizeData。

因为 AuthorizationApplicationModelProvider 类对 AuthorizationPolicy.CombineAsync 静态方法有依赖，这里不得不做一个类似的 PermissionAuthorizationApplicationModelProvider 类，在本类实现 CombineAsync 方法。暂且不论该方法放在本类是否合适的问题。

       public static AuthorizeFilter GetFilter(IAuthorizationPolicyProvider policyProvider, IEnumerable<IAuthorizeData> authData)
       {
           // The default policy provider will make the same policy for given input, so make it only once.
           // This will always execute synchronously.
           if (policyProvider.GetType() == typeof(DefaultAuthorizationPolicyProvider))
           {
               var policy = CombineAsync(policyProvider, authData).GetAwaiter().GetResult();
               return new AuthorizeFilter(policy);
           }
           else
           {
               return new AuthorizeFilter(policyProvider, authData);
           }
       }
       private static async Task<AuthorizationPolicy> CombineAsync(IAuthorizationPolicyProvider policyProvider, IEnumerable<IAuthorizeData> authorizeData)
       {
           if (policyProvider == null)
           {
               throw new ArgumentNullException(nameof(policyProvider));
           }
           if (authorizeData == null)
           {
               throw new ArgumentNullException(nameof(authorizeData));
           }
           var policyBuilder = new AuthorizationPolicyBuilder();
           var any = false;
           foreach (var authorizeDatum in authorizeData)
           {
               any = true;
               var useDefaultPolicy = true;
               if (!string.IsNullOrWhiteSpace(authorizeDatum.Policy))
               {
                   var policy = await policyProvider.GetPolicyAsync(authorizeDatum.Policy);
                   if (policy == null)
                   {
                       //throw new InvalidOperationException(Resources.FormatException_AuthorizationPolicyNotFound(authorizeDatum.Policy));
                       throw new InvalidOperationException(nameof(authorizeDatum.Policy));
                   }
policyBuilder.Combine(policy);
                   useDefaultPolicy = false;
               }
               var rolesSplit = authorizeDatum.Roles?.Split(',');
               if (rolesSplit != null && rolesSplit.Any())
               {
                   var trimmedRolesSplit = rolesSplit.Where(r => !string.IsNullOrWhiteSpace(r)).Select(r => r.Trim());
                   policyBuilder.RequireRole(trimmedRolesSplit);
                   useDefaultPolicy = false;
               }
               if(authorizeDatum is IPermissionAuthorizeData permissionAuthorizeDatum )
               {
                   var groupsSplit = permissionAuthorizeDatum.Groups?.Split(',');
                   if (groupsSplit != null && groupsSplit.Any())
                   {
                       var trimmedGroupsSplit = groupsSplit.Where(r => !string.IsNullOrWhiteSpace(r)).Select(r => r.Trim());
                       policyBuilder.RequireClaim("Group", trimmedGroupsSplit); // TODO: 注意硬编码
                       useDefaultPolicy = false;
                   }
                   var permissionsSplit = permissionAuthorizeDatum.Permissions?.Split(',');
                   if (permissionsSplit != null && permissionsSplit.Any())
                   {
                       var trimmedPermissionsSplit = permissionsSplit.Where(r => !string.IsNullOrWhiteSpace(r)).Select(r => r.Trim());
                       policyBuilder.RequireClaim("Permission", trimmedPermissionsSplit);// TODO: 注意硬编码
                       useDefaultPolicy = false;
                   }
               }
               var authTypesSplit = authorizeDatum.AuthenticationSchemes?.Split(',');
               if (authTypesSplit != null && authTypesSplit.Any())
               {
                   foreach (var authType in authTypesSplit)
                   {
                       if (!string.IsNullOrWhiteSpace(authType))
                       {
                           policyBuilder.AuthenticationSchemes.Add(authType.Trim());
                       }
                   }
               }
               if (useDefaultPolicy)
               {
policyBuilder.Combine(await policyProvider.GetDefaultPolicyAsync());
               }
           }
           return any ? policyBuilder.Build() : null;
       }

if(authorizeDatum is IPermissionAuthorizeData permissionAuthorizeDatum ) 为扩展部分。

四、Startup

1 2	services.AddMvc(); services.Replac(ServiceDescriptor.Transient<IApplicationModelProvider,PermissionAuthorizationApplicationModelProvider>());

五、Jwt 示例

[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
    private readonly JwtSecurityTokenHandler _tokenHandler = new JwtSecurityTokenHandler();
    [HttpGet]
    [Route("SignIn")]
    public async Task<ActionResult<string>> SignIn()
    {
        var user = new ClaimsPrincipal(new ClaimsIdentity(new[]
        {
            // 备注：Claim Type: Group 和 Permission 这里使用的是硬编码，应该定义为类似于 ClaimTypes.Role 的常量；另外，下列模拟数据不一定合逻辑。
            new Claim(ClaimTypes.Name, "Bob"),
            new Claim(ClaimTypes.Role, "经理"),  // 注意：不能使用逗号分隔来达到多个角色的目的，下同。
            new Claim(ClaimTypes.Role, "副经理"),
            new Claim("Group", "研发部"),
            new Claim("Group", "生产部"),
            new Claim("Permission", "请假审批"),
            new Claim("Permission", "权限1"),
            new Claim("Permission", "权限2"),
        }, JwtBearerDefaults.AuthenticationScheme));
        var token = new JwtSecurityToken(
            "SignalRAuthenticationSample",
            "SignalRAuthenticationSample",
            user.Claims,
            expires: DateTime.UtcNow.AddDays(30),
            signingCredentials: SignatureHelper.GenerateSigningCredentials("1234567890123456"));
        return _tokenHandler.WriteToken(token);
    }
    [HttpGet]
    [Route("Test")]
    [PermissionAuthorize(Groups = "研发部,生产部", Roles = "经理", Permissions = "请假审批"] // 研发部经理或生成部经理，并且有请假审批的权限。Groups 、Roles 和 Permission 是 `And` 的关系。
    public async Task<ActionResult<IEnumerable<string>>> Test()
    {
        var user = HttpContext.User;
        return new string[] { "value1", "value2" };
    }
 }

六、问题

AuthorizeFilter 类显示实现了 IFilterFactory 接口的 CreateInstance 方法：

IFilterMetadata IFilterFactory.CreateInstance(IServiceProvider serviceProvider)
{
    if (Policy != null || PolicyProvider != null)
    {
        // The filter is fully constructed. Use the current instance to authorize.
        return this;
    }
 
    Debug.Assert(AuthorizeData != null);
    var policyProvider = serviceProvider.GetRequiredService<IAuthorizationPolicyProvider>();
    return AuthorizationApplicationModelProvider.GetFilter(policyProvider, AuthorizeData);
}

竟然对 AuthorizationApplicationModelProvider.GetFilter 静态方法产生了依赖。庆幸的是，如果通过 AuthorizeFilter(IAuthorizationPolicyProvider policyProvider, IEnumerable<IAuthorizeData> authorizeData) 或 AuthorizeFilter(AuthorizationPolicy policy) 创建 AuthorizeFilter 对象不会产生什么不良影响。

七、下一步

[PermissionAuthorize(Groups = "研发部,生产部", Roles = "经理", Permissions = "请假审批"] 这种形式还是不够灵活，哪怕用多个 Attribute, And 和 Or 的逻辑组合不一定能满足需求。可以在 IPermissionAuthorizeData 新增一个 Rule 属性，实现类似的效果：

1	[PermissionAuthorize(Rule = "(Groups:研发部,生产部)&&(Roles:请假审批\|\|Permissions:超级权限)"]

通过 Rule 计算复杂的授权。

八、如果通过自定义 IAuthorizationPolicyProvider 实现？

另一种方式是自定义 IAuthorizationPolicyProvider ，不过还需要自定义 AuthorizeFilter。因为当不是使用 DefaultAuthorizationPolicyProvider 而是自定义 IAuthorizationPolicyProvider 时，AuthorizationApplicationModelProvider（或前文定义的 PermissionAuthorizationApplicationModelProvider）会使用 AuthorizeFilter(IAuthorizationPolicyProvider policyProvider, IEnumerable<IAuthorizeData> authorizeData) 创建 AuthorizeFilter 对象，而不是 AuthorizeFilter(AuthorizationPolicy policy)。这会造成 AuthorizeFilter 对象在 OnAuthorizationAsync 时会间接调用 AuthorizationPolicy.CombineAsync 静态方法。

这可以说是一个设计上的缺陷，不应该让 AuthorizationPolicy.CombineAsync 静态方法存在，哪怕提供个 IAuthorizationPolicyCombiner 也好。另外，上文提到的 AuthorizationApplicationModelProvider.GetFilter 静态方法同样不是一种好的设计。等微软想通吧。

参考资料

https://docs.microsoft.com/zh-cn/aspnet/core/security/authorization/iauthorizationpolicyprovider?view=aspnetcore-2.1

排版问题：http://blog.tubumu.com/2018/11/28/aspnetcore-mvc-extend-authorization/