【ASP.NET Core】運行原理(4):授權

本系列將分析ASP.NET Core運行原理 "【ASP.NET Core】運行原理(1):創建WebHost" "【ASP.NET Core】運行原理(2):啟動WebHost" "【ASP.NET Core】運行原理(3):認證" 【ASP.NET Core】運行原理(4):授權在認證階段通過 ...

本系列將分析ASP.NET Core運行原理

在認證階段通過用戶令牌獲取到用戶的Claims，而授權就是對這些Claims的驗證。

授權核心

services.AddAuthorization(opt => opt.AddPolicy("isAdmin", builder => builder.RequireUserName("admin")));
通過上面的代碼，可以添加一個isAdmin的授權。

對於第一個參數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;
    }
}

實際上，AuthorizationOptions相當於AuthorizationPolicy的集合
而AuthorizationPolicy則是一個具體的授權策略對象

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

而AuthorizationPolicyBuilder通過Build方法可以構建一個AuthorizationPolicy，其內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是授權策略AuthorizationPolicy的一個授權條件,策略下的所有授權條件滿足，則授權成功。

public interface IAuthorizationRequirement
{
}

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

IAuthorizationHandler是授權條件IAuthorizationRequirement的具體處理器，授權條件下的任意1個處理器授權成功，則授權成功。(預設情況下：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;
    }
}

授權的最終實現代碼在IAuthorizationHandler

執行授權

解釋了授權策略的原理，再談談授權策略的觸發。通常我們在MVC中使用授權功能，而觸發授權也是在註冊MVC代碼中，一併註冊了。

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用來描述MVC中的模型，而IApplicationModelProvider則是初始化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會初始化ApplicationModel的授權部分，註冊到Filters屬性上（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方法會在Action執行前觸發，內部調用IPolicyEvaluator執行

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，將合併policy的所有scheme認證結果。
在AuthorizeAsync方法中，將調用IAuthorizationService來實現授權。

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類中，將調用policy的所有Requirement的Handle處理

總結

授權核心：AuthorizationOptions、AuthorizationPolicy、AuthorizationPolicyBuilder

AuthorizationOptions 用於保存 AuthorizationPolicy
AuthorizationPolicyBuilder 用於創建 AuthorizationPolicy
AuthorizationPolicy 包含 IAuthorizationRequirement 和 AuthenticationSchemes
IAuthorizationRequirement 包含授權邏輯 IAuthorizationHandler

執行授權：AuthorizeFilter、IPolicyEvaluator、IAuthorizationService

AuthorizeFilter的OnAuthorizationAsync方法會在Action執行前觸發，內部調用IPolicyEvaluator執行
IPolicyEvaluator 先根據 Schemes 獲取Claims，然後調用 IAuthorizationService 的授權方法
IAuthorizationService 調用 Requirement 對應的Handle授權邏輯

個人覺得源碼的一個待優化的地方：在DefaultAuthorizationHandlerProvider的GetHandlersAsync方法按需返回IAuthorizationHandler更合適。

本文鏈接：http://www.cnblogs.com/neverc/p/8204339.html

【ASP.NET Core】運行原理(4):授權

目錄

授權核心

執行授權

總結