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
      
    };
  });
}

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));
  } 

 .....
}

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;
  }
 }

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>();
  }
 }

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"color: #ff0000">　　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) "htmlcode">

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())"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 "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 "color: #ff0000">　　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


                                
                                

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