追本溯源，从使用开始
首先看一下我们通常是如何使用微软自带的认证，一般在Startup里面配置我们所需的依赖认证服务，这里通过JWT的认证方式讲解
public void ConfigureServices(IServiceCollection services) { services.AddAuthentication(authOpt => { authOpt.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme; authOpt.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme; }) .AddJwtBearer(o => { o.TokenValidationParameters = new TokenValidationParameters { //配置自己所要验证的参数 }; }); }
我们来看一下源码AddAuthentication主要做了什么
public static class AuthenticationServiceCollectionExtensions { public static AuthenticationBuilder AddAuthentication( this IServiceCollection services, Action<AuthenticationOptions> configureOptions) { if (services == null) throw new ArgumentNullException(nameof (services)); if (configureOptions == null) throw new ArgumentNullException(nameof (configureOptions)); AuthenticationBuilder authenticationBuilder = services.AddAuthentication(); services.Configure<AuthenticationOptions>(configureOptions); return authenticationBuilder; } public static AuthenticationBuilder AddAuthentication( this IServiceCollection services) { if (services == null) throw new ArgumentNullException(nameof (services)); services.AddAuthenticationCore(); services.AddDataProtection(); services.AddWebEncoders(); services.TryAddSingleton<ISystemClock, SystemClock>(); return new AuthenticationBuilder(services); } public static AuthenticationBuilder AddAuthentication( this IServiceCollection services, string defaultScheme) { return services.AddAuthentication((Action<AuthenticationOptions>) (o => o.DefaultScheme = defaultScheme)); } ..... }
ConfigureServices方法基本都是服务的注册，基于微软的风格，这里的AddAuthenticationCore肯定是我们的认证服务注册方法，来看一下
public static class AuthenticationCoreServiceCollectionExtensions { /// <summary> /// Add core authentication services needed for <see cref="T:Microsoft.AspNetCore.Authentication.IAuthenticationService" />. /// </summary> public static IServiceCollection AddAuthenticationCore( this IServiceCollection services) { if (services == null) throw new ArgumentNullException(nameof (services)); services.TryAddScoped<IAuthenticationService, AuthenticationService>(); services.TryAddSingleton<IClaimsTransformation, NoopClaimsTransformation>(); services.TryAddScoped<IAuthenticationHandlerProvider, AuthenticationHandlerProvider>(); services.TryAddSingleton<IAuthenticationSchemeProvider, AuthenticationSchemeProvider>(); return services; } /// <summary> /// Add core authentication services needed for <see cref="T:Microsoft.AspNetCore.Authentication.IAuthenticationService" />. /// </summary> public static IServiceCollection AddAuthenticationCore( this IServiceCollection services, Action<AuthenticationOptions> configureOptions) { if (services == null) throw new ArgumentNullException(nameof (services)); if (configureOptions == null) throw new ArgumentNullException(nameof (configureOptions)); services.AddAuthenticationCore(); services.Configure<AuthenticationOptions>(configureOptions); return services; } }
我们看到这里主要注册了AuthenticationService, AuthenticationHandlerProvider, AuthenticationSchemeProvider这三个对象，如文章开头所说，追本溯源，从使用开始，我们先看一下这三个对象是如何在认证体系中使用的，且是如何发挥作用的。
从使用开始
看一下我们的认证管道构建
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory) { ... app.UseAuthentication(); ... } public static class AuthAppBuilderExtensions { public static IApplicationBuilder UseAuthentication( this IApplicationBuilder app) { if (app == null) throw new ArgumentNullException(nameof (app)); return app.UseMiddleware<AuthenticationMiddleware>(); } }
这里使用了约定的注册方式UseMiddleware，并且指定使用中间件AuthenticationMiddleware
public class AuthenticationMiddleware { private readonly RequestDelegate _next; public AuthenticationMiddleware(RequestDelegate next, IAuthenticationSchemeProvider schemes) { if (next == null) throw new ArgumentNullException(nameof (next)); if (schemes == null) throw new ArgumentNullException(nameof (schemes)); this._next = next; this.Schemes = schemes; } public IAuthenticationSchemeProvider Schemes { get; set; } public async Task Invoke(HttpContext context) { context.Features.Set<IAuthenticationFeature>((IAuthenticationFeature) new AuthenticationFeature() { OriginalPath = context.Request.Path, OriginalPathBase = context.Request.PathBase }); IAuthenticationHandlerProvider handlers = context.RequestServices.GetRequiredService<IAuthenticationHandlerProvider>(); foreach (AuthenticationScheme authenticationScheme in await this.Schemes.GetRequestHandlerSchemesAsync()) { IAuthenticationRequestHandler handlerAsync = await handlers.GetHandlerAsync(context, authenticationScheme.Name) as IAuthenticationRequestHandler; bool flag = handlerAsync != null; if (flag) flag = await handlerAsync.HandleRequestAsync(); if (flag) return; } AuthenticationScheme authenticateSchemeAsync = await this.Schemes.GetDefaultAuthenticateSchemeAsync(); if (authenticateSchemeAsync != null) { AuthenticateResult authenticateResult = await context.AuthenticateAsync(authenticateSchemeAsync.Name); //实际的认证业务 if (authenticateResult?.Principal != null) context.User = authenticateResult.Principal; } await this._next(context); } }
在继续往下之前，我们先看一下这个认证中间件的作用结果，当认证通过时，在HttpContext的User属性（ClaimPrincipal）赋予身份标识，所以在后续的请求管道中都是基于认证结果中的身份标识做鉴权，这个我们会在后面的实际操作中会提到。
言归正传，在这里引出了我们的两个对象AuthenticationHandlerProvider, AuthenticationSchemeProvider。
重要对象讲解
IAuthenticationSchemeProvider
从名字来看，IAuthenticationSchemeProvider的作用应该是提供Scheme的，这也是Provider在微软的风格里面起的作用（类似于工厂模式）。
这个Scheme是什么呢？很明显，在Framework时代，也是有基于不同Scheme验证的，比如Bearer，Cookie，在Aspnet Core中定义不同的Scheme代表着不同的认证处理方式，具体体现是在每个Scheme中包含对应的IAuthenticationHandler类型的Handler，由它来完成跟自身Scheme相关的认证处理。如果没有定义会怎么样？仔细看上面这块源码，只有当AuthenticationScheme不为空时才会做认证，否则一旦在Controller打上鉴权标签[Authorize]，将会直接返回401，所以我们必须指定自己的Scheme。
那么我们在哪里指定我们的Scheme类似呢？我们先返回到ConfigureService的AddJwtBearer，使用过的朋友们肯定知道，这里获取的Scheme是我们在ConfigureService通过Addxxx scheme指定的Scheme类型。这里我们是使用JWT的
在这里指定了TOptions 为JwtBearerOptions，而THandler为JwtBearerHandler。
public virtual AuthenticationBuilder AddScheme<TOptions, THandler>( string authenticationScheme, string displayName, Action<TOptions> configureOptions) where TOptions : AuthenticationSchemeOptions, new() where THandler : AuthenticationHandler<TOptions> { return this.AddSchemeHelper<TOptions, THandler>(authenticationScheme, displayName, configureOptions); } private AuthenticationBuilder AddSchemeHelper<TOptions, THandler>( string authenticationScheme, string displayName, Action<TOptions> configureOptions) where TOptions : class, new() where THandler : class, IAuthenticationHandler { this.Services.Configure<AuthenticationOptions>((Action<AuthenticationOptions>) (o => o.AddScheme(authenticationScheme, (Action<AuthenticationSchemeBuilder>) (scheme => { scheme.HandlerType = typeof (THandler); scheme.DisplayName = displayName; })))); if (configureOptions != null) this.Services.Configure<TOptions>(authenticationScheme, configureOptions); this.Services.AddTransient<THandler>(); return this; }
注意这里TOptions 是需要继承AuthenticationSchemeOptions的，在这里是JwtBearerOptions，而THandler是AuthenticationHandler<TOptions>类型的Handler，在这里是JwtBearerHandler。
我们回到Scheme的分析继续往下，首先看一下AuthenticationScheme的定义
public class AuthenticationScheme { /// <summary>Constructor.</summary> public AuthenticationScheme(string name, string displayName, Type handlerType) { if (name == null) throw new ArgumentNullException(nameof (name)); if (handlerType == (Type) null) throw new ArgumentNullException(nameof (handlerType)); if (!typeof (IAuthenticationHandler).IsAssignableFrom(handlerType)) throw new ArgumentException("handlerType must implement IAuthenticationHandler."); this.Name = name; this.HandlerType = handlerType; this.DisplayName = displayName; } /// <summary>The name of the authentication scheme.</summary> public string Name { get; } /// <summary> /// The display name for the scheme. Null is valid and used for non user facing schemes. /// </summary> public string DisplayName { get; } /// <summary> /// The <see cref="T:Microsoft.AspNetCore.Authentication.IAuthenticationHandler" /> type that handles this scheme. /// </summary> public Type HandlerType { get; } }
在这里可以看到，如果要使用Aspnet Core自身的认证体系，需先注册Scheme，并且该Scheme必须指定一个类型为IAuthenticationHandler的Handler，否则会抛出异常。（这个其实在AddxxxScheme的时候已经指定了AuthenticationHandler）
我们再看一下IAuthenticationSchemeProvider的GetRequestHandlerSchemesAsync方法做了什么
public virtual Task<IEnumerable<AuthenticationScheme>> GetRequestHandlerSchemesAsync() { return Task.FromResult<IEnumerable<AuthenticationScheme>>((IEnumerable<AuthenticationScheme>) this._requestHandlers); }
这东西返回了_requestHandlers，这是什么？看代码
public class AuthenticationSchemeProvider : IAuthenticationSchemeProvider { private readonly object _lock = new object(); private readonly AuthenticationOptions _options; private readonly IDictionary<string, AuthenticationScheme> _schemes; private readonly List<AuthenticationScheme> _requestHandlers; /// <summary> /// Creates an instance of <see cref="T:Microsoft.AspNetCore.Authentication.AuthenticationSchemeProvider" /> /// using the specified <paramref name="options" />, /// </summary> public AuthenticationSchemeProvider(IOptions<AuthenticationOptions> options) : this(options, (IDictionary<string, AuthenticationScheme>) new Dictionary<string, AuthenticationScheme>((IEqualityComparer<string>) StringComparer.Ordinal)) { } /// <summary> /// Creates an instance of <see cref="T:Microsoft.AspNetCore.Authentication.AuthenticationSchemeProvider" /> /// using the specified <paramref name="options" /> and <paramref name="schemes" />. /// </summary> protected AuthenticationSchemeProvider( IOptions<AuthenticationOptions> options, IDictionary<string, AuthenticationScheme> schemes) { this._options = options.Value; IDictionary<string, AuthenticationScheme> dictionary = schemes; if (dictionary == null) throw new ArgumentNullException(nameof (schemes)); this._schemes = dictionary; this._requestHandlers = new List<AuthenticationScheme>(); foreach (AuthenticationSchemeBuilder scheme in this._options.Schemes) this.AddScheme(scheme.Build()); } public virtual void AddScheme(AuthenticationScheme scheme) { if (this._schemes.ContainsKey(scheme.Name)) throw new InvalidOperationException("Scheme already exists: " + scheme.Name); lock (this._lock) { if (this._schemes.ContainsKey(scheme.Name)) throw new InvalidOperationException("Scheme already exists: " + scheme.Name); if (typeof (IAuthenticationRequestHandler).IsAssignableFrom(scheme.HandlerType)) this._requestHandlers.Add(scheme); this._schemes[scheme.Name] = scheme; } } ..... }
这东西就是把我们在认证注册服务中指定的scheme，通过解析出的AuthenticationSchemeProvider 的构造函数加载来的，进而返回一系列的List<AuthenticationScheme>，OK拿到这些scheme之后有什么用呢？这里引出了我们的第二个对象AuthenticationHandlerProvider，下面我们来了解一下。
IAuthenticationHandlerProvider
我们看到，AuthenticationMiddleware中用到了IAuthenticationHandlerProvider的GetHandlerAsync方法，那我们先看一下这个方法的作用
public class AuthenticationHandlerProvider : IAuthenticationHandlerProvider { private Dictionary<string, IAuthenticationHandler> _handlerMap = new Dictionary<string, IAuthenticationHandler>((IEqualityComparer<string>) StringComparer.Ordinal); /// <summary>Constructor.</summary> public AuthenticationHandlerProvider(IAuthenticationSchemeProvider schemes) { this.Schemes = schemes; } /// <summary> /// The <see cref="T:Microsoft.AspNetCore.Authentication.IAuthenticationHandlerProvider" />. /// </summary> public IAuthenticationSchemeProvider Schemes { get; } /// <summary>Returns the handler instance that will be used.</summary> public async Task<IAuthenticationHandler> GetHandlerAsync( HttpContext context, string authenticationScheme) { if (this._handlerMap.ContainsKey(authenticationScheme)) return this._handlerMap[authenticationScheme]; AuthenticationScheme schemeAsync = await this.Schemes.GetSchemeAsync(authenticationScheme); if (schemeAsync == null) return (IAuthenticationHandler) null; IAuthenticationHandler handler = (context.RequestServices.GetService(schemeAsync.HandlerType) ?? ActivatorUtilities.CreateInstance(context.RequestServices, schemeAsync.HandlerType)) as IAuthenticationHandler; if (handler != null) { await handler.InitializeAsync(schemeAsync, context); this._handlerMap[authenticationScheme] = handler; } return handler; } }
在创建Handler的时候，是先从AuthenticationScheme中获取，如果不存在则通过ActivatorUtilities创建。 获取到Handle后，将会放在_handlerMap字典里面， 当下次获取Handler的时候，将直接从缓存中获取。
IAuthenticationService
这个对象是在AuthenticationMiddleware中最后才用到的，而且是基于HttpContext的扩展被调用
public static class AuthenticationHttpContextExtensions { public static Task<AuthenticateResult> AuthenticateAsync(this HttpContext context, string scheme) => context.RequestServices.GetRequiredService<IAuthenticationService>().AuthenticateAsync(context, scheme); .... }
这里主要调用了IAuthenticationService的AuthenticateAsync方法，看一下这个方法做了什么
public class AuthenticationService : IAuthenticationService { public IAuthenticationSchemeProvider Schemes { get; } public IAuthenticationHandlerProvider Handlers { get; } public IClaimsTransformation Transform { get; } public virtual async Task<AuthenticateResult> AuthenticateAsync(HttpContext context, string scheme) { if (scheme == null) { var scheme = (await this.Schemes.GetDefaultAuthenticateSchemeAsync())?.Name; if (scheme == null) throw new InvalidOperationException($"No authenticationScheme was specified, and there was no DefaultAuthenticateScheme found."); } var handler = await Handlers.GetHandlerAsync(context, scheme); if(handler == null) throw await this.CreateMissingHandlerException(scheme); AuthenticateResult result = await handler.AuthenticateAsync(); if (result != null && result.Succeeded) return AuthenticateResult.Success(new AuthenticationTicket(await Transform.TransformAsync(result.Principal), result.Properties, result.Ticket.AuthenticationScheme)); return result; } }
这里其实就是我们在前面讲的根据Scheme获取对应的AuthenticationHandler，然后调用AuthenticateAsync()方法，这个方法调用了核心方法HandleAuthenticateOnceAsync，然后再调用HandleAuthenticateAsync()这个核心的认证方法。
从上图看到这个HandleAuthenticateAsync是个抽象方法，我们的子类都需要实现这个方法的动作，基于本文的例子，我们看一下JwtBearerHandler的一个实际认证。
public class JwtBearerHandler : AuthenticationHandler<JwtBearerOptions> { protected override async Task<AuthenticateResult> HandleAuthenticateAsync() { JwtBearerHandler jwtBearerHandler = this; string token = (string) null; object obj; AuthenticationFailedContext authenticationFailedContext; int num; try { MessageReceivedContext messageReceivedContext = new MessageReceivedContext(jwtBearerHandler.Context, jwtBearerHandler.Scheme, jwtBearerHandler.Options); await jwtBearerHandler.Events.MessageReceived(messageReceivedContext); if (messageReceivedContext.Result != null) return messageReceivedContext.Result; token = messageReceivedContext.Token; if (string.IsNullOrEmpty(token)) { string header = (string) jwtBearerHandler.Request.Headers["Authorization"]; if (string.IsNullOrEmpty(header)) return AuthenticateResult.NoResult(); if (header.StartsWith("Bearer ", StringComparison.OrdinalIgnoreCase)) token = header.Substring("Bearer ".Length).Trim(); if (string.IsNullOrEmpty(token)) return AuthenticateResult.NoResult(); } if (jwtBearerHandler._configuration == null && jwtBearerHandler.Options.ConfigurationManager != null) { OpenIdConnectConfiguration configurationAsync = await jwtBearerHandler.Options.ConfigurationManager.GetConfigurationAsync(jwtBearerHandler.Context.RequestAborted); jwtBearerHandler._configuration = configurationAsync; } TokenValidationParameters validationParameters1 = jwtBearerHandler.Options.TokenValidationParameters.Clone(); if (jwtBearerHandler._configuration != null) { string[] strArray = new string[1] { jwtBearerHandler._configuration.Issuer }; TokenValidationParameters validationParameters2 = validationParameters1; IEnumerable<string> validIssuers = validationParameters1.get_ValidIssuers(); object obj1 = (validIssuers != null ? (object) validIssuers.Concat<string>((IEnumerable<string>) strArray) : (object) null) ?? (object) strArray; validationParameters2.set_ValidIssuers((IEnumerable<string>) obj1); TokenValidationParameters validationParameters3 = validationParameters1; IEnumerable<SecurityKey> issuerSigningKeys = validationParameters1.get_IssuerSigningKeys(); IEnumerable<SecurityKey> securityKeys = (issuerSigningKeys != null ? issuerSigningKeys.Concat<SecurityKey>((IEnumerable<SecurityKey>) jwtBearerHandler._configuration.get_SigningKeys()) : (IEnumerable<SecurityKey>) null) ?? (IEnumerable<SecurityKey>) jwtBearerHandler._configuration.get_SigningKeys(); validationParameters3.set_IssuerSigningKeys(securityKeys); } List<Exception> exceptionList = (List<Exception>) null; foreach (ISecurityTokenValidator securityTokenValidator in (IEnumerable<ISecurityTokenValidator>) jwtBearerHandler.Options.SecurityTokenValidators) { if (securityTokenValidator.CanReadToken(token)) { SecurityToken securityToken; ClaimsPrincipal claimsPrincipal; try { claimsPrincipal = securityTokenValidator.ValidateToken(token, validationParameters1, ref securityToken); } catch (Exception ex) { jwtBearerHandler.Logger.TokenValidationFailed(ex); if (jwtBearerHandler.Options.RefreshOnIssuerKeyNotFound && jwtBearerHandler.Options.ConfigurationManager != null && ex is SecurityTokenSignatureKeyNotFoundException) jwtBearerHandler.Options.ConfigurationManager.RequestRefresh(); if (exceptionList == null) exceptionList = new List<Exception>(1); exceptionList.Add(ex); continue; } jwtBearerHandler.Logger.TokenValidationSucceeded(); TokenValidatedContext validatedContext = new TokenValidatedContext(jwtBearerHandler.Context, jwtBearerHandler.Scheme, jwtBearerHandler.Options); validatedContext.Principal = claimsPrincipal; validatedContext.SecurityToken = securityToken; TokenValidatedContext tokenValidatedContext = validatedContext; await jwtBearerHandler.Events.TokenValidated(tokenValidatedContext); if (tokenValidatedContext.Result != null) return tokenValidatedContext.Result; if (jwtBearerHandler.Options.SaveToken) tokenValidatedContext.Properties.StoreTokens((IEnumerable<AuthenticationToken>) new AuthenticationToken[1] { new AuthenticationToken() { Name = "access_token", Value = token } }); tokenValidatedContext.Success(); return tokenValidatedContext.Result; } } if (exceptionList == null) return AuthenticateResult.Fail("No SecurityTokenValidator available for token: " + token ?? "[null]"); authenticationFailedContext = new AuthenticationFailedContext(jwtBearerHandler.Context, jwtBearerHandler.Scheme, jwtBearerHandler.Options) { Exception = exceptionList.Count == 1 ? exceptionList[0] : (Exception) new AggregateException((IEnumerable<Exception>) exceptionList) }; await jwtBearerHandler.Events.AuthenticationFailed(authenticationFailedContext); return authenticationFailedContext.Result == null ? AuthenticateResult.Fail(authenticationFailedContext.Exception) : authenticationFailedContext.Result; } catch (Exception ex) { obj = (object) ex; num = 1; } if (num == 1) { Exception ex = (Exception) obj; jwtBearerHandler.Logger.ErrorProcessingMessage(ex); authenticationFailedContext = new AuthenticationFailedContext(jwtBearerHandler.Context, jwtBearerHandler.Scheme, jwtBearerHandler.Options) { Exception = ex }; await jwtBearerHandler.Events.AuthenticationFailed(authenticationFailedContext); if (authenticationFailedContext.Result != null) return authenticationFailedContext.Result; Exception source = obj as Exception; if (source == null) throw obj; ExceptionDispatchInfo.Capture(source).Throw(); authenticationFailedContext = (AuthenticationFailedContext) null; } obj = (object) null; token = (string) null; AuthenticateResult authenticateResult; return authenticateResult; } }
这个方法有点长，主要是从Request.Headers里面获取Authorization的Bearer出来解析，再在AddJwtBearer中传入的委托参数JwtBearerOptions的TokenValidationParameters属性作为依据进行对比来进行认证是否通过与否。
总结
本文对 ASP.NET Core 的认证流程做了一个源码分析流程介绍，由于是源码分析篇，所以可能会比较枯燥和苦涩难懂。在后面的真正使用过程中，然后再结合本篇的一个总结流程，相信大家会逐渐开朗。
- 在Startup类中的ConfigureServices方法通过添加AddAuthentication注册我们最主要的三个对象AuthenticationService, AuthenticationHandlerProvider, AuthenticationSchemeProvider
- 通过AddAuthentication返回的AuthenticationBuilder 通过AddJwtBearer（或者AddCookie）来指定Scheme类型和需要验证的参数
- 在Startup类中的Configure方法通过添加UseAuthentication注册认证中间件
- 在认证过程中，通过AuthenticationSchemeProvider获取正确的Scheme，在AuthenticationService中通过Scheme和AuthenticationHandlerProvider获取正确的AuthenticationHandler，最后通过对应的AuthenticationHandler的AuthenticateAsync方法进行认证流程