ASP.NET Core[源码分析篇] - 认证

　　追本溯源，从使用开始　　

　　首先看一下我们的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。

　　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。

1. 在ConfigureServices中通过添加AddAuthentication注册我们最主要的三个对象AuthenticationService, AuthenticationHandlerProvider, AuthenticationSchemeProvider
2. 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
3. 在Configure通过添加UseAuthentication注册认证中间件
4. 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