一、前言

IdentityServer4已經分享了一些應用實戰的文章，從架構到授權中心的落地應用，也伴隨著對IdentityServer4掌握了一些使用規則，但是很多原理性東西還是一知半解，故我這裡持續性來帶大家一起來解讀它的相關原始碼，本文先來看看為什麼Controller或者Action中新增Authorize或者全域性中新增AuthorizeFilter過濾器就可以實現該資源受到保護，需要通過access_token才能通過相關的授權呢？今天我帶大家來了解AuthorizeAttribute和AuthorizeFilter的關係及程式碼解讀。

二、程式碼解讀

解讀之前我們先來看看下面兩種標註授權方式的程式碼：

標註方式

 [Authorize]
 [HttpGet]
 public async Task<object> Get()
 {
      var userId = User.UserId();
      return new
      {
         name = User.Name(),
         userId = userId,
         displayName = User.DisplayName(),
         merchantId = User.MerchantId(),
      };
 }

程式碼中通過[Authorize]標註來限制該api資源的訪問

全域性方式

public void ConfigureServices(IServiceCollection services)
{
     //全域性新增AuthorizeFilter 過濾器方式
     services.AddControllers(options=>options.Filters.Add(new AuthorizeFilter()));

     services.AddAuthorization();
     services.AddAuthentication("Bearer")
         .AddIdentityServerAuthentication(options =>
         {
             options.Authority = "http://localhost:5000";    //配置Identityserver的授權地址
             options.RequireHttpsMetadata = false;           //不需要https    
             options.ApiName = OAuthConfig.UserApi.ApiName;  //api的name，需要和config的名稱相同
         });
}
 

全域性通過新增AuthorizeFilter過濾器方式進行全域性api資源的限制

AuthorizeAttribute

先來看看AuthorizeAttribute原始碼：

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
public class AuthorizeAttribute : Attribute, IAuthorizeData
{
    /// <summary>
    /// Initializes a new instance of the <see cref="AuthorizeAttribute"/> class. 
    /// </summary>
    public AuthorizeAttribute() { }

    /// <summary>
    /// Initializes a new instance of the <see cref="AuthorizeAttribute"/> class with the specified policy. 
    /// </summary>
    /// <param name="policy">The name of the policy to require for authorization.</param>
    public AuthorizeAttribute(string policy)
    {
       Policy = policy;
    }

    /// <summary>
    /// 收取策略
    /// </summary>
    public string Policy { get; set; }

    /// <summary>
    /// 授權角色
    /// </summary>
    public string Roles { get; set; }

    /// <summary>
    /// 授權Schemes
    /// </summary>
    public string AuthenticationSchemes { get; set; }
}

程式碼中可以看到AuthorizeAttribute繼承了IAuthorizeData抽象介面，該介面主要是授權資料的約束定義，定義了三個資料屬性

• Prolicy ：授權策略
• Roles : 授權角色
• AuthenticationSchemes ：授權Schemes 的支援
  Asp.Net Core 中的http中介軟體會根據IAuthorizeData這個來獲取有哪些授權過濾器，來實現過濾器的攔截並執行相關程式碼。
  我們看看AuthorizeAttribute程式碼如下：

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; }
}

我們再來看看授權中介軟體（UseAuthorization）的核心程式碼：

public static IApplicationBuilder UseAuthorization(this IApplicationBuilder app)
{
    if (app == null)
    {
        throw new ArgumentNullException(nameof(app));
    }

    VerifyServicesRegistered(app);

    return app.UseMiddleware<AuthorizationMiddleware>();
}

程式碼中註冊了AuthorizationMiddleware這個中介軟體，AuthorizationMiddleware中介軟體原始碼如下：

 public class AuthorizationMiddleware
 {
        // Property key is used by Endpoint routing to determine if Authorization has run
        private const string AuthorizationMiddlewareInvokedWithEndpointKey = "__AuthorizationMiddlewareWithEndpointInvoked";
        private static readonly object AuthorizationMiddlewareWithEndpointInvokedValue = new object();

        private readonly RequestDelegate _next;
        private readonly IAuthorizationPolicyProvider _policyProvider;

        public AuthorizationMiddleware(RequestDelegate next, IAuthorizationPolicyProvider policyProvider)
        {
            _next = next ?? throw new ArgumentNullException(nameof(next));
            _policyProvider = policyProvider ?? throw new ArgumentNullException(nameof(policyProvider));
        }

        public async Task Invoke(HttpContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            var endpoint = context.GetEndpoint();

            if (endpoint != null)
            {
                // EndpointRoutingMiddleware uses this flag to check if the Authorization middleware processed auth metadata on the endpoint.
                // The Authorization middleware can only make this claim if it observes an actual endpoint.
                context.Items[AuthorizationMiddlewareInvokedWithEndpointKey] = AuthorizationMiddlewareWithEndpointInvokedValue;
            }

            // 通過終結點路由元素IAuthorizeData來獲得對於的AuthorizeAttribute並關聯到AuthorizeFilter中
            var authorizeData = endpoint?.Metadata.GetOrderedMetadata<IAuthorizeData>() ?? Array.Empty<IAuthorizeData>();
            var policy = await AuthorizationPolicy.CombineAsync(_policyProvider, authorizeData);
            if (policy == null)
            {
                await _next(context);
                return;
            }

            // Policy evaluator has transient lifetime so it fetched from request services instead of injecting in constructor
            var policyEvaluator = context.RequestServices.GetRequiredService<IPolicyEvaluator>();

            var authenticateResult = await policyEvaluator.AuthenticateAsync(policy, context);

            // Allow Anonymous skips all authorization
            if (endpoint?.Metadata.GetMetadata<IAllowAnonymous>() != null)
            {
                await _next(context);
                return;
            }

            // Note that the resource will be null if there is no matched endpoint
            var authorizeResult = await policyEvaluator.AuthorizeAsync(policy, authenticateResult, context, resource: endpoint);

            if (authorizeResult.Challenged)
            {
                if (policy.AuthenticationSchemes.Any())
                {
                    foreach (var scheme in policy.AuthenticationSchemes)
                    {
                        await context.ChallengeAsync(scheme);
                    }
                }
                else
                {
                    await context.ChallengeAsync();
                }

                return;
            }
            else if (authorizeResult.Forbidden)
            {
                if (policy.AuthenticationSchemes.Any())
                {
                    foreach (var scheme in policy.AuthenticationSchemes)
                    {
                        await context.ForbidAsync(scheme);
                    }
                }
                else
                {
                    await context.ForbidAsync();
                }

                return;
            }

            await _next(context);
        }
    }

程式碼中核心攔截並獲得AuthorizeFilter過濾器的程式碼

var authorizeData = endpoint?.Metadata.GetOrderedMetadata<IAuthorizeData>() ?? Array.Empty<IAuthorizeData>();

前面我分享過一篇關於 Asp.Net Core EndPoint 終結點路由工作原理解讀 的文章裡面講解到通過EndPoint終結點路由來獲取Controller和Action中的Attribute特性標註，這裡也是通過該方法來攔截獲取對於的AuthorizeAttribute的.
而獲取到相關authorizeData授權資料後，下面的一系列程式碼都是通過判斷來進行AuthorizeAsync授權執行的方法,這裡就不詳細分享它的授權認證的過程了。
細心的同學應該已經發現上面的程式碼有一個比較特殊的程式碼：

if (endpoint?.Metadata.GetMetadata<IAllowAnonymous>() != null)
{
      await _next(context);
      return;
}

程式碼中通過endpoint終結點路由來獲取是否標註有AllowAnonymous的特性，如果有則直接執行下一個中介軟體，不進行下面的AuthorizeAsync授權認證方法，
這也是為什麼Controller和Action上標註AllowAnonymous可以跳過授權認證的原因了。

AuthorizeFilter 原始碼

有的人會問AuthorizeAttirbute和AuthorizeFilter有什麼關係呢？它們是一個東西嗎？
我們再來看看AuthorizeFilter原始碼，程式碼如下：

public class AuthorizeFilter : IAsyncAuthorizationFilter, IFilterFactory
{
        /// <summary>
        /// Initializes a new <see cref="AuthorizeFilter"/> instance.
        /// </summary>
        public AuthorizeFilter()
            : this(authorizeData: new[] { new AuthorizeAttribute() })
        {
        }

        /// <summary>
        /// Initialize a new <see cref="AuthorizeFilter"/> instance.
        /// </summary>
        /// <param name="policy">Authorization policy to be used.</param>
        public AuthorizeFilter(AuthorizationPolicy policy)
        {
            if (policy == null)
            {
                throw new ArgumentNullException(nameof(policy));
            }

            Policy = policy;
        }

        /// <summary>
        /// Initialize a new <see cref="AuthorizeFilter"/> instance.
        /// </summary>
        /// <param name="policyProvider">The <see cref="IAuthorizationPolicyProvider"/> to use to resolve policy names.</param>
        /// <param name="authorizeData">The <see cref="IAuthorizeData"/> to combine into an <see cref="IAuthorizeData"/>.</param>
        public AuthorizeFilter(IAuthorizationPolicyProvider policyProvider, IEnumerable<IAuthorizeData> authorizeData)
            : this(authorizeData)
        {
            if (policyProvider == null)
            {
                throw new ArgumentNullException(nameof(policyProvider));
            }

            PolicyProvider = policyProvider;
        }

        /// <summary>
        /// Initializes a new instance of <see cref="AuthorizeFilter"/>.
        /// </summary>
        /// <param name="authorizeData">The <see cref="IAuthorizeData"/> to combine into an <see cref="IAuthorizeData"/>.</param>
        public AuthorizeFilter(IEnumerable<IAuthorizeData> authorizeData)
        {
            if (authorizeData == null)
            {
                throw new ArgumentNullException(nameof(authorizeData));
            }

            AuthorizeData = authorizeData;
        }

        /// <summary>
        /// Initializes a new instance of <see cref="AuthorizeFilter"/>.
        /// </summary>
        /// <param name="policy">The name of the policy to require for authorization.</param>
        public AuthorizeFilter(string policy)
            : this(new[] { new AuthorizeAttribute(policy) })
        {
        }

        /// <summary>
        /// The <see cref="IAuthorizationPolicyProvider"/> to use to resolve policy names.
        /// </summary>
        public IAuthorizationPolicyProvider PolicyProvider { get; }

        /// <summary>
        /// The <see cref="IAuthorizeData"/> to combine into an <see cref="IAuthorizeData"/>.
        /// </summary>
        public IEnumerable<IAuthorizeData> AuthorizeData { get; }

        /// <summary>
        /// Gets the authorization policy to be used.
        /// </summary>
        /// <remarks>
        /// If<c>null</c>, the policy will be constructed using
        /// <see cref="AuthorizationPolicy.CombineAsync(IAuthorizationPolicyProvider, IEnumerable{IAuthorizeData})"/>.
        /// </remarks>
        public AuthorizationPolicy Policy { get; }

        bool IFilterFactory.IsReusable => true;

        // Computes the actual policy for this filter using either Policy or PolicyProvider + AuthorizeData
        private Task<AuthorizationPolicy> ComputePolicyAsync()
        {
            if (Policy != null)
            {
                return Task.FromResult(Policy);
            }

            if (PolicyProvider == null)
            {
                throw new InvalidOperationException(
                    Resources.FormatAuthorizeFilter_AuthorizationPolicyCannotBeCreated(
                        nameof(AuthorizationPolicy),
                        nameof(IAuthorizationPolicyProvider)));
            }

            return AuthorizationPolicy.CombineAsync(PolicyProvider, AuthorizeData);
        }

        internal async Task<AuthorizationPolicy> GetEffectivePolicyAsync(AuthorizationFilterContext context)
        {
            // Combine all authorize filters into single effective policy that's only run on the closest filter
            var builder = new AuthorizationPolicyBuilder(await ComputePolicyAsync());
            for (var i = 0; i < context.Filters.Count; i++)
            {
                if (ReferenceEquals(this, context.Filters[i]))
                {
                    continue;
                }

                if (context.Filters[i] is AuthorizeFilter authorizeFilter)
                {
                    // Combine using the explicit policy, or the dynamic policy provider
                    builder.Combine(await authorizeFilter.ComputePolicyAsync());
                }
            }

            var endpoint = context.HttpContext.GetEndpoint();
            if (endpoint != null)
            {
                // When doing endpoint routing, MVC does not create filters for any authorization specific metadata i.e [Authorize] does not
                // get translated into AuthorizeFilter. Consequently, there are some rough edges when an application uses a mix of AuthorizeFilter
                // explicilty configured by the user (e.g. global auth filter), and uses endpoint metadata.
                // To keep the behavior of AuthFilter identical to pre-endpoint routing, we will gather auth data from endpoint metadata
                // and produce a policy using this. This would mean we would have effectively run some auth twice, but it maintains compat.
                var policyProvider = PolicyProvider ?? context.HttpContext.RequestServices.GetRequiredService<IAuthorizationPolicyProvider>();
                var endpointAuthorizeData = endpoint.Metadata.GetOrderedMetadata<IAuthorizeData>() ?? Array.Empty<IAuthorizeData>();

                var endpointPolicy = await AuthorizationPolicy.CombineAsync(policyProvider, endpointAuthorizeData);
                if (endpointPolicy != null)
                {
                    builder.Combine(endpointPolicy);
                }
            }

            return builder.Build();
        }

        /// <inheritdoc />
        public virtual async Task OnAuthorizationAsync(AuthorizationFilterContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            if (!context.IsEffectivePolicy(this))
            {
                return;
            }

            // IMPORTANT: Changes to authorization logic should be mirrored in security's AuthorizationMiddleware
            var effectivePolicy = await GetEffectivePolicyAsync(context);
            if (effectivePolicy == null)
            {
                return;
            }

            var policyEvaluator = context.HttpContext.RequestServices.GetRequiredService<IPolicyEvaluator>();

            var authenticateResult = await policyEvaluator.AuthenticateAsync(effectivePolicy, context.HttpContext);

            // Allow Anonymous skips all authorization
            if (HasAllowAnonymous(context))
            {
                return;
            }

            var authorizeResult = await policyEvaluator.AuthorizeAsync(effectivePolicy, authenticateResult, context.HttpContext, context);

            if (authorizeResult.Challenged)
            {
                context.Result = new ChallengeResult(effectivePolicy.AuthenticationSchemes.ToArray());
            }
            else if (authorizeResult.Forbidden)
            {
                context.Result = new ForbidResult(effectivePolicy.AuthenticationSchemes.ToArray());
            }
        }

        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);
        }

        private static bool HasAllowAnonymous(AuthorizationFilterContext context)
        {
            var filters = context.Filters;
            for (var i = 0; i < filters.Count; i++)
            {
                if (filters[i] is IAllowAnonymousFilter)
                {
                    return true;
                }
            }

            // When doing endpoint routing, MVC does not add AllowAnonymousFilters for AllowAnonymousAttributes that
            // were discovered on controllers and actions. To maintain compat with 2.x,
            // we'll check for the presence of IAllowAnonymous in endpoint metadata.
            var endpoint = context.HttpContext.GetEndpoint();
            if (endpoint?.Metadata?.GetMetadata<IAllowAnonymous>() != null)
            {
                return true;
            }

            return false;
        }
    }

程式碼中繼承了 IAsyncAuthorizationFilter, IFilterFactory兩個抽象介面，分別來看看這兩個抽象介面的原始碼

IAsyncAuthorizationFilter原始碼如下：

/// <summary>
/// A filter that asynchronously confirms request authorization.
/// </summary>
public interface IAsyncAuthorizationFilter : IFilterMetadata
{
    ///定義了授權的方法
    Task OnAuthorizationAsync(AuthorizationFilterContext context);
}

IAsyncAuthorizationFilter程式碼中繼承了IFilterMetadata介面，同時定義了OnAuthorizationAsync抽象方法,子類需要實現該方法，然而AuthorizeFilter中也已經實現了該方法，稍後再來詳細講解該方法，我們再繼續看看IFilterFactory抽象介面,程式碼如下：

public interface IFilterFactory : IFilterMetadata
 {
       
    bool IsReusable { get; }

    //建立IFilterMetadata 物件方法
    IFilterMetadata CreateInstance(IServiceProvider serviceProvider);
}

我們回到AuthorizeFilter 原始碼中，該原始碼中提供了四個構造初始化方法同時包含了AuthorizeData、Policy屬性，我們看看它的預設構造方法程式碼

public class AuthorizeFilter : IAsyncAuthorizationFilter, IFilterFactory
{
        public IEnumerable<IAuthorizeData> AuthorizeData { get; }

        //預設建構函式中預設建立了AuthorizeAttribute 物件
        public AuthorizeFilter()
            : this(authorizeData: new[] { new AuthorizeAttribute() })
        {
        }

        //賦值AuthorizeData
        public AuthorizeFilter(IEnumerable<IAuthorizeData> authorizeData)
        {
            if (authorizeData == null)
            {
                throw new ArgumentNullException(nameof(authorizeData));
            }

            AuthorizeData = authorizeData;
        }
}

上面的程式碼中預設的建構函式預設給構建了一個AuthorizeAttribute物件，並且賦值給了IEnumerable<IAuthorizeData>的集合屬性;
好了，看到這裡AuthorizeFilter過濾器也是預設構造了一個AuthorizeAttribute的物件，也就是構造了授權所需要的IAuthorizeData資訊.
同時AuthorizeFilter實現的OnAuthorizationAsync方法中通過GetEffectivePolicyAsync這個方法獲得有效的授權策略，並且進行下面的授權AuthenticateAsync的執行
AuthorizeFilter程式碼中提供了HasAllowAnonymous方法來實現是否Controller或者Action上標註了AllowAnonymous特性，用於跳過授權
HasAllowAnonymous程式碼如下：

private static bool HasAllowAnonymous(AuthorizationFilterContext context)
{
     var filters = context.Filters;
     for (var i = 0; i < filters.Count; i++)
     {
        if (filters[i] is IAllowAnonymousFilter)
        {
           return true;
        }
     }
     //同樣通過上下文的endpoint 來獲取是否標註了AllowAnonymous特性
     var endpoint = context.HttpContext.GetEndpoint();
     if (endpoint?.Metadata?.GetMetadata<IAllowAnonymous>() != null)
     {
        return true;
     }

     return false;
}

到這裡我們再回到全域性新增過濾器的方式程式碼：

 services.AddControllers(options=>options.Filters.Add(new AuthorizeFilter()));

分析到這裡 ，我很是好奇，它是怎麼全域性新增進去的呢？我開啟原始碼看了下，原始碼如下：

public class MvcOptions : IEnumerable<ICompatibilitySwitch>
{

        public MvcOptions()
        {
            CacheProfiles = new Dictionary<string, CacheProfile>(StringComparer.OrdinalIgnoreCase);
            Conventions = new List<IApplicationModelConvention>();
            Filters = new FilterCollection();
            FormatterMappings = new FormatterMappings();
            InputFormatters = new FormatterCollection<IInputFormatter>();
            OutputFormatters = new FormatterCollection<IOutputFormatter>();
            ModelBinderProviders = new List<IModelBinderProvider>();
            ModelBindingMessageProvider = new DefaultModelBindingMessageProvider();
            ModelMetadataDetailsProviders = new List<IMetadataDetailsProvider>();
            ModelValidatorProviders = new List<IModelValidatorProvider>();
            ValueProviderFactories = new List<IValueProviderFactory>();
        }

        //過濾器集合
        public FilterCollection Filters { get; }
}

FilterCollection相關核心程式碼如下：

public class FilterCollection : Collection<IFilterMetadata>
{
        
        public IFilterMetadata Add<TFilterType>() where TFilterType : IFilterMetadata
        {
            return Add(typeof(TFilterType));
        }

        //其他核心程式碼為貼出來
}

程式碼中提供了Add方法，約束了IFilterMetadata型別的物件，這也是上面的過濾器中為什麼都繼承了IFilterMetadata的原因。
到這裡程式碼解讀和實現原理已經分析完了，如果有分析不到位之處還請多多指教！！！

結論：授權中介軟體通過獲取IAuthorizeData來獲取AuthorizeAttribute物件相關的授權資訊，並構造授權策略物件進行授權認證的，而AuthorizeFilter過濾器也會預設新增AuthorizeAttribute的授權相關資料IAuthorizeData並實現OnAuthorizationAsync方法，同時中介軟體中通過授權策略提供者IAuthorizationPolicyProvider來獲得對於的授權策略進行授權認