【ASP.NET Core】运行原理(4):授权

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本系列将分析ASP.NET Core运行原理

【ASP.NET Core】运行原理(1):创建WebHost 【ASP.NET Core】运行原理(2):启动WebHost 【ASP.NET Core】运行原理(3):认证 【ASP.NET Core】运行原理(4):授权

在认证阶段通过用户令牌获取到用户的Claims，而授权就是对这些Claims的验证。

目录 授权核心 AuthorizationOptions AuthorizationPolicy AuthorizationPolicyBuilder 执行授权 AuthorizeFilter IPolicyEvaluator IAuthorizationService 总结 授权核心

services.AddAuthorization(opt => opt.AddPolicy("isAdmin", builder => builder.RequireUserName("admin")));
通过上面的代码，可以添加一个isAdmin的授权。

对于第一个参数opt：

public class AuthorizationOptions
{
    private IDictionary<string, AuthorizationPolicy> PolicyMap { get; } = new Dictionary<string, AuthorizationPolicy>();

    public void AddPolicy(string name, AuthorizationPolicy policy)
    {
        PolicyMap[name] = policy;
    }

    public void AddPolicy(string name, Action<AuthorizationPolicyBuilder> configurePolicy)
    {
        var policyBuilder = new AuthorizationPolicyBuilder();
        configurePolicy(policyBuilder);
        AddPolicy(name,policyBuilder.Build());
    }

    public AuthorizationPolicy GetPolicy(string name)
    {
        return PolicyMap.ContainsKey(name) ? PolicyMap[name] : null;
    }
}

实际上，AuthorizationOptions相当于AuthorizationPolicy的集合
而AuthorizationPolicy则是一个具体的授权策略对象

public class AuthorizationPolicy
{
    public IReadOnlyList<IAuthorizationRequirement> Requirements { get; }
    public IReadOnlyList<string> AuthenticationSchemes { get; }
}

而AuthorizationPolicyBuilder通过Build方法可以构建一个AuthorizationPolicy，其内部有很多常用的添加IAuthorizationRequirement的方法：

public AuthorizationPolicy Build()
{
    return new AuthorizationPolicy(this.Requirements, this.AuthenticationSchemes);
}
public AuthorizationPolicyBuilder RequireUserName(string userName)
{
    this.Requirements.Add(new NameAuthorizationRequirement(userName));
}

... Require() ...

IAuthorizationRequirement是授权策略AuthorizationPolicy的一个授权条件,策略下的所有授权条件满足，则授权成功。

public interface IAuthorizationRequirement
{
}

public class NameAuthorizationRequirement : IAuthorizationRequirement
{
    public string RequiredName { get; }
}

IAuthorizationHandler是授权条件IAuthorizationRequirement的具体处理器，授权条件下的任意1个处理器授权成功，则授权成功。(默认情况下：AuthorizationOptions的InvokeHandlersAfterFailure = true)

public interface IAuthorizationHandler
{
    Task HandleAsync(AuthorizationHandlerContext context);
}

public abstract class AuthorizationHandler<TRequirement> : IAuthorizationHandler where TRequirement : IAuthorizationRequirement
{
    public virtual async Task HandleAsync(AuthorizationHandlerContext context)
    {
        foreach (TRequirement requirement in context.Requirements)
            await HandleRequirementAsync(context, requirement);
    }

    protected abstract Task HandleRequirementAsync(AuthorizationHandlerContext context, TRequirement requirement);
}

public class NameAuthorizationRequirement : AuthorizationHandler<NameAuthorizationRequirement>
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, NameAuthorizationRequirement requirement)
    {
        if (context.User?.Identities.Any(identity => identity.Name == requirement.RequiredName))
            context.Succeed((IAuthorizationRequirement) requirement);
        return Task.CompletedTask;
    }
}

授权的最终实现代码在IAuthorizationHandler

执行授权

解释了授权策略的原理，再谈谈授权策略的触发。通常我们在MVC中使用授权功能，而触发授权也是在注册MVC代码中，一并注册了。

public static IMvcBuilder AddMvc(this IServiceCollection services)
{
    IMvcCoreBuilder builder = services.AddMvcCore();
    builder.AddAuthorization();
}

internal static void AddAuthorizationServices(IServiceCollection services)
{
    services.AddAuthenticationCore();
    services.AddAuthorization();
    services.AddAuthorizationPolicyEvaluator();
    services.TryAddEnumerable(ServiceDescriptor.Transient<IApplicationModelProvider, AuthorizationApplicationModelProvider>());
}

在MVC中，ApplicationModel用来描述MVC中的模型，而IApplicationModelProvider则是初始化MVC的模型:

public class ApplicationModel
{
    public IList<ControllerModel> Controllers { get; }

    public IList<IFilterMetadata> Filters { get; }
}
public interface IApplicationModelProvider
{
    int Order { get; }
    void OnProvidersExecuting(ApplicationModelProviderContext context);
    void OnProvidersExecuted(ApplicationModelProviderContext context);
}

其中AuthorizationApplicationModelProvider会初始化ApplicationModel的授权部分，注册到Filters属性上（AuthorizeFilter 和 AllowAnonymousFilter）。

public interface IAsyncAuthorizationFilter : IFilterMetadata
{
    Task OnAuthorizationAsync(AuthorizationFilterContext context);
}

public class AuthorizeFilter : IAsyncAuthorizationFilter
{
    public virtual async Task OnAuthorizationAsync(AuthorizationFilterContext context)
    {
        var policyEvaluator = GetRequiredService<IPolicyEvaluator>();
        var authenticationResult = await policyEvaluator.AuthenticateAsync(effectivePolicy, context.HttpContext);
        var authorizationResult = await policyEvaluator.AuthorizeAsync(effectivePolicy, authenticationResult, context.HttpContext, context);
        if (authorizationResult.Challenged)
        {
            context.Result = (IActionResult) new ChallengeResult((IList<string>) effectivePolicy.AuthenticationSchemes.ToArray<string>());
        }
        else if (authorizationResult.Forbidden)
        {
            context.Result = (IActionResult) new ForbidResult((IList<string>) effectivePolicy.AuthenticationSchemes.ToArray<string>());
        }
    }
}

AuthorizeFilter的OnAuthorizationAsync方法会在Action执行前触发，内部调用IPolicyEvaluator执行

public interface IPolicyEvaluator
{
    Task<AuthenticateResult> AuthenticateAsync(AuthorizationPolicy policy, HttpContext context);
    Task<PolicyAuthorizationResult> AuthorizeAsync(AuthorizationPolicy policy, AuthenticateResult authenticationResult, HttpContext context, object resource);
}

public class PolicyEvaluator : IPolicyEvaluator
{
    private readonly IAuthorizationService _authorization;
    public virtual async Task<AuthenticateResult> AuthenticateAsync(AuthorizationPolicy policy, HttpContext context)
    {
    }
    public virtual async Task<PolicyAuthorizationResult> AuthorizeAsync(AuthorizationPolicy policy, AuthenticateResult authenticationResult, HttpContext context, object resource)
    {
        var result = await _authorization.AuthorizeAsync(context.User, resource, policy);
        if (result.Succeeded) return PolicyAuthorizationResult.Success();
        return (authenticationResult.Succeeded) ? PolicyAuthorizationResult.Forbid() : PolicyAuthorizationResult.Challenge();
    }
}

在AuthenticateAsync方法中，将合并policy的所有scheme认证结果。
在AuthorizeAsync方法中，将调用IAuthorizationService来实现授权。

public interface IAuthorizationService
{
    Task<AuthorizationResult> AuthorizeAsync(ClaimsPrincipal user, object resource, IEnumerable<IAuthorizationRequirement> requirements);
    Task<AuthorizationResult> AuthorizeAsync(ClaimsPrincipal user, object resource, string policyName);
}

public class DefaultAuthorizationService : IAuthorizationService
{
    public async Task<AuthorizationResult> AuthorizeAsync(ClaimsPrincipal user, object resource, string policyName)
    {
        var policy = await _policyProvider.GetPolicyAsync(policyName);
        return await this.AuthorizeAsync(user, resource, policy);
    }

    public async Task<AuthorizationResult> AuthorizeAsync(ClaimsPrincipal user, object resource, IEnumerable<IAuthorizationRequirement> requirements)
    {
        var authContext = _contextFactory.CreateContext(requirements, user, resource);
        var handlers = await _handlers.GetHandlersAsync(authContext);
        foreach (var handler in handlers)
        {
            await handler.HandleAsync(authContext);
            if (!_options.InvokeHandlersAfterFailure && authContext.HasFailed)
                break;
        }
        return _evaluator.Evaluate(authContext);
    }
}

在IAuthorizationService类中，将调用policy的所有Requirement的Handle处理

总结

授权核心：AuthorizationOptions、AuthorizationPolicy、AuthorizationPolicyBuilder

AuthorizationOptions 用于保存 AuthorizationPolicy
AuthorizationPolicyBuilder 用于创建 AuthorizationPolicy
AuthorizationPolicy 包含 IAuthorizationRequirement 和 AuthenticationSchemes
IAuthorizationRequirement 包含授权逻辑 IAuthorizationHandler

执行授权：AuthorizeFilter、IPolicyEvaluator、IAuthorizationService

AuthorizeFilter的OnAuthorizationAsync方法会在Action执行前触发，内部调用IPolicyEvaluator执行
IPolicyEvaluator 先根据 Schemes 获取Claims，然后调用 IAuthorizationService 的授权方法
IAuthorizationService 调用 Requirement 对应的Handle授权逻辑

个人觉得源码的一个待优化的地方：在DefaultAuthorizationHandlerProvider的GetHandlersAsync方法按需返回IAuthorizationHandler更合适。

本文链接：http://www.cnblogs.com/neverc/p/8204339.html

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