Asp.Net Core Authorize你不知道的那些事（源码解读）
一、前言
IdentityServer4已经分享了一些应用实战的文章，从架构到授权中心的落地应用，也伴随着对IdentityServer4掌握了一些使用规则，但是很多原理性东西还是一知半解，故我这里持续性来带大家一起来解读它的相关源代码，本文先来看看为什么Controller或者Action中添加Authorize或者全局中添加AuthorizeFilter过滤器就可以实现该资源受到保护，需要通过access_token才能通过相关的授权呢？今天我带大家来了解AuthorizeAttribute和AuthorizeFilter的关系及代码解读。
二、代码解读
解读之前我们先来看看下面两种标注授权方式的代码：
标注方式
[Authorize]
[HttpGet]
public async Task
var userId = User.UserId();
return new
{
name = User.Name(),
userId = userId,
displayName = User.DisplayName(),
merchantId = User.MerchantId(),
};}
代码中通过[Authorize]标注来限制该api资源的访问
全局方式
public void ConfigureServices(IServiceCollection services)
{
//全局添加AuthorizeFilter 过滤器方式
services.AddControllers(options=>options.Filters.Add(new AuthorizeFilter()));
services.AddAuthorization();
services.AddAuthentication("Bearer")
.AddIdentityServerAuthentication(options =>
{
options.Authority = "http://localhost:5000"; //配置Identityserver的授权地址
options.RequireHttpsMetadata = false; //不需要https
options.ApiName = OAuthConfig.UserApi.ApiName; //api的name，需要和config的名称相同
});}
全局通过添加AuthorizeFilter过滤器方式进行全局api资源的限制
AuthorizeAttribute
先来看看AuthorizeAttribute源代码：
[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>
/// 授权角色
/// </summary>
public string Roles { get; set; }
/// <summary>
/// 授权Schemes
/// </summary>
public string AuthenticationSchemes { get; set; }}
代码中可以看到AuthorizeAttribute继承了IAuthorizeData抽象接口，该接口主要是授权数据的约束定义，定义了三个数据属性
Prolicy ：授权策略
Roles : 授权角色
AuthenticationSchemes ：授权Schemes 的支持
Asp.Net Core 中的http中间件会根据IAuthorizeData这个来获取有哪些授权过滤器，来实现过滤器的拦截并执行相关代码。
我们看看AuthorizeAttribute代码如下：
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; }}
我们再来看看授权中间件（UseAuthorization）的核心代码：
public static IApplicationBuilder UseAuthorization(this IApplicationBuilder app)
{
if (app == null)
{
throw new ArgumentNullException(nameof(app));
}
VerifyServicesRegistered(app);
return app.UseMiddleware<AuthorizationMiddleware>();}
代码中注册了AuthorizationMiddleware这个中间件，AuthorizationMiddleware中间件源代码如下：
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;
}
// 通过终结点路由元素IAuthorizeData来获得对于的AuthorizeAttribute并关联到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);
}
}代码中核心拦截并获得AuthorizeFilter过滤器的代码
var authorizeData = endpoint?.Metadata.GetOrderedMetadata() ?? Array.Empty();
前面我分享过一篇关于 Asp.Net Core EndPoint 终结点路由工作原理解读 的文章里面讲解到通过EndPoint终结点路由来获取Controller和Action中的Attribute特性标注，这里也是通过该方法来拦截获取对于的AuthorizeAttribute的.
而获取到相关authorizeData授权数据后，下面的一系列代码都是通过判断来进行AuthorizeAsync授权执行的方法,这里就不详细分享它的授权认证的过程了。
细心的同学应该已经发现上面的代码有一个比较特殊的代码：
if (endpoint?.Metadata.GetMetadata() != null)
{
await _next(context);
return;}
代码中通过endpoint终结点路由来获取是否标注有AllowAnonymous的特性，如果有则直接执行下一个中间件，不进行下面的AuthorizeAsync授权认证方法，
这也是为什么Controller和Action上标注AllowAnonymous可以跳过授权认证的原因了。
AuthorizeFilter 源码
有的人会问AuthorizeAttirbute和AuthorizeFilter有什么关系呢？它们是一个东西吗？
我们再来看看AuthorizeFilter源代码，代码如下：
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;
}
}代码中继承了 IAsyncAuthorizationFilter, IFilterFactory两个抽象接口，分别来看看这两个抽象接口的源代码
IAsyncAuthorizationFilter源代码如下：
///
/// A filter that asynchronously confirms request authorization.
///
public interface IAsyncAuthorizationFilter : IFilterMetadata
{
///定义了授权的方法
Task OnAuthorizationAsync(AuthorizationFilterContext context);}
IAsyncAuthorizationFilter代码中继承了IFilterMetadata接口，同时定义了OnAuthorizationAsync抽象方法,子类需要实现该方法，然而AuthorizeFilter中也已经实现了该方法，稍后再来详细讲解该方法，我们再继续看看IFilterFactory抽象接口,代码如下：
public interface IFilterFactory : IFilterMetadata
{
bool IsReusable { get; }
//创建IFilterMetadata 对象方法
IFilterMetadata CreateInstance(IServiceProvider serviceProvider);}
我们回到AuthorizeFilter 源代码中，该源代码中提供了四个构造初始化方法同时包含了AuthorizeData、Policy属性，我们看看它的默认构造方法代码
public class AuthorizeFilter : IAsyncAuthorizationFilter, IFilterFactory
{
public IEnumerable<IAuthorizeData> AuthorizeData { get; }
//默认构造函数中默认创建了AuthorizeAttribute 对象
public AuthorizeFilter()
: this(authorizeData: new[] { new AuthorizeAttribute() })
{
}
//赋值AuthorizeData
public AuthorizeFilter(IEnumerable<IAuthorizeData> authorizeData)
{
if (authorizeData == null)
{
throw new ArgumentNullException(nameof(authorizeData));
}
AuthorizeData = authorizeData;
}}
上面的代码中默认的构造函数默认给构建了一个AuthorizeAttribute对象，并且赋值给了IEnumerable的集合属性;
好了，看到这里AuthorizeFilter过滤器也是默认构造了一个AuthorizeAttribute的对象，也就是构造了授权所需要的IAuthorizeData信息.
同时AuthorizeFilter实现的OnAuthorizationAsync方法中通过GetEffectivePolicyAsync这个方法获得有效的授权策略，并且进行下面的授权AuthenticateAsync的执行
AuthorizeFilter代码中提供了HasAllowAnonymous方法来实现是否Controller或者Action上标注了AllowAnonymous特性，用于跳过授权
HasAllowAnonymous代码如下：
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;
}
}
//同样通过上下文的endpoint 来获取是否标注了AllowAnonymous特性
var endpoint = context.HttpContext.GetEndpoint();
if (endpoint?.Metadata?.GetMetadata<IAllowAnonymous>() != null)
{
return true;
}
return false;}
到这里我们再回到全局添加过滤器的方式代码：
services.AddControllers(options=>options.Filters.Add(new AuthorizeFilter()));
分析到这里 ，我很是好奇，它是怎么全局添加进去的呢？我打开源代码看了下，源代码如下：
public class MvcOptions : IEnumerable
{
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>();
}
//过滤器集合
public FilterCollection Filters { get; }}
FilterCollection相关核心代码如下：
public class FilterCollection : Collection
{
public IFilterMetadata Add<TFilterType>() where TFilterType : IFilterMetadata
{
return Add(typeof(TFilterType));
}
//其他核心代码为贴出来}
代码中提供了Add方法，约束了IFilterMetadata类型的对象，这也是上面的过滤器中为什么都继承了IFilterMetadata的原因。
到这里代码解读和实现原理已经分析完了，如果有分析不到位之处还请多多指教！！！
结论：授权中间件通过获取IAuthorizeData来获取AuthorizeAttribute对象相关的授权信息，并构造授权策略对象进行授权认证的，而AuthorizeFilter过滤器也会默认添加AuthorizeAttribute的授权相关数据IAuthorizeData并实现OnAuthorizationAsync方法，同时中间件中通过授权策略提供者IAuthorizationPolicyProvider来获得对于的授权策略进行授权认证.
作者：Jlion
