Azure配置功能管理器：调用IsEnabled时向自定义FeatureFilter传参

我之前正好在项目里处理过类似的需求，不管是Web应用还是Azure函数/WebJob场景，都有对应的解决方案，下面一步步给你讲清楚：

核心思路 #

默认的IFeatureManager.IsEnabled方法提供了重载，可以传递额外的运行时参数，这些参数会被传入自定义过滤器的Evaluate方法的FeatureFilterEvaluationContext中。我们只需要调整过滤器的逻辑，既可以兼容原来的HttpContext场景，也能接收手动传递的参数。

步骤1：修改自定义FeatureFilter #

首先调整你的AllowedUsersFeatureFilter，让它支持两种参数来源：HttpContext（Web应用）和手动传递的参数（函数/WebJob/后台任务）。这里我们可以把IHttpContextAccessor设为可选注入，同时从context.Parameters中读取额外参数：

using Microsoft.FeatureManagement;
using Microsoft.FeatureManagement.FeatureFilters;
using System.Security.Claims;
using System.Collections.Generic;
using System.Linq;
using System;

// 过滤器的配置参数（从App Configuration读取）
public class AllowedUsersFilterSettings
{
    public string Aliases { get; set; }
}

// 用于传递运行时用户参数的类
public class UserRuntimeParams
{
    public string UserAlias { get; set; }
}

[FilterAlias("AllowedUsers")]
public class AllowedUsersFeatureFilter : IFeatureFilter
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    // 把IHttpContextAccessor设为可选，兼容非Web场景
    public AllowedUsersFeatureFilter(IHttpContextAccessor httpContextAccessor = null)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public bool Evaluate(FeatureFilterEvaluationContext context)
    {
        // 先读取从App Configuration配置的过滤器参数
        var filterSettings = context.Parameters.Get<AllowedUsersFilterSettings>();
        if (filterSettings == null || string.IsNullOrWhiteSpace(filterSettings.Aliases))
            return false;

        string userAlias = null;

        // 优先读取手动传递的运行时参数
        var runtimeParams = context.Parameters.Get<UserRuntimeParams>();
        if (runtimeParams != null && !string.IsNullOrWhiteSpace(runtimeParams.UserAlias))
        {
            userAlias = runtimeParams.UserAlias;
        }
        // 没有传递参数时，再尝试从HttpContext获取（Web应用场景）
        else if (_httpContextAccessor?.HttpContext != null)
        {
            var userEmail = _httpContextAccessor.HttpContext.User?.FindFirst(ClaimTypes.Upn)?.Value;
            userAlias = userEmail?.Split('@').FirstOrDefault();
        }

        if (string.IsNullOrWhiteSpace(userAlias))
            return false;

        // 检查用户别名是否在允许列表中
        return filterSettings.Aliases.Split(',')
            .Select(a => a.Trim())
            .Contains(userAlias, StringComparer.OrdinalIgnoreCase);
    }
}

步骤2：调用IsEnabled时传递参数 #

根据不同的场景，调用方式略有不同：

Web应用场景（兼容HttpContext和手动传参） #

如果还是依赖HttpContext，直接调用无参数的重载即可：

bool isEnabled = await _featureManager.IsEnabledAsync("YourFeatureName");

如果需要手动传参（比如后台任务、测试），使用带参数字典的重载：

// 构造运行时参数
var runtimeParams = new UserRuntimeParams { UserAlias = "john_doe" };
var parameters = new Dictionary<string, string>();
// 用AddJson扩展方法把对象序列化为JSON存入参数（需要引用Microsoft.Extensions.Configuration.AzureAppConfiguration）
parameters.AddJson(nameof(UserRuntimeParams), runtimeParams);

bool isEnabled = await _featureManager.IsEnabledAsync("YourFeatureName", parameters);

或者直接用键值对传递：

var parameters = new Dictionary<string, string>
{
    { "UserAlias", "john_doe" }
};
// 过滤器里可以用context.Parameters["UserAlias"]获取
bool isEnabled = await _featureManager.IsEnabledAsync("YourFeatureName", parameters);

Azure函数应用场景 #

Azure函数（尤其是隔离进程模型）没有HttpContext，必须手动传递参数。首先在Program.cs中配置Feature Manager：

using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.FeatureManagement;
using Microsoft.Extensions.Configuration.AzureAppConfiguration;

var host = new HostBuilder()
    .ConfigureFunctionsWorkerDefaults()
    .ConfigureServices(services =>
    {
        // 添加Azure App Configuration并启用功能管理
        services.AddAzureAppConfiguration(options =>
        {
            options.Connect("<你的App Configuration连接字符串>")
                   .UseFeatureFlags();
        })
        .AddFeatureManagement()
        .AddFeatureFilter<AllowedUsersFeatureFilter>();

        // 非Web场景不需要注册IHttpContextAccessor
        // services.AddHttpContextAccessor();
    })
    .Build();

host.Run();

然后在函数中注入IFeatureManager并传递参数：

using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.FeatureManagement;
using System.Collections.Generic;
using System.Threading.Tasks;

public class FeatureFlagFunction
{
    private readonly IFeatureManager _featureManager;

    public FeatureFlagFunction(IFeatureManager featureManager)
    {
        _featureManager = featureManager;
    }

    [Function("CheckFeature")]
    public async Task<HttpResponseData> Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get")] HttpRequestData req)
    {
        // 从请求中获取用户别名（比如查询参数）
        req.Query.TryGetValue("userAlias", out var userAlias);

        // 构造参数
        var parameters = new Dictionary<string, string>
        {
            { "UserAlias", userAlias }
        };

        bool isEnabled = await _featureManager.IsEnabledAsync("YourFeatureName", parameters);

        var response = req.CreateResponse();
        await response.WriteAsJsonAsync(new { IsFeatureEnabled = isEnabled });
        return response;
    }
}

Azure WebJob场景 #

WebJob的实现和函数类似，同样在Program.cs中配置Feature Manager，然后在Job类中注入IFeatureManager：

using Microsoft.Extensions.Hosting;
using Microsoft.FeatureManagement;
using System.Threading.Tasks;

public class Program
{
    public static void Main()
    {
        var host = new HostBuilder()
            .ConfigureServices(services =>
            {
                services.AddAzureAppConfiguration(options =>
                {
                    options.Connect("<你的App Configuration连接字符串>")
                           .UseFeatureFlags();
                })
                .AddFeatureManagement()
                .AddFeatureFilter<AllowedUsersFeatureFilter>();

                services.AddHostedService<MyWebJob>();
            })
            .Build();

        host.Run();
    }
}

public class MyWebJob : IHostedService
{
    private readonly IFeatureManager _featureManager;
    private readonly IHostApplicationLifetime _appLifetime;

    public MyWebJob(IFeatureManager featureManager, IHostApplicationLifetime appLifetime)
    {
        _featureManager = featureManager;
        _appLifetime = appLifetime;
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        // 假设从队列/数据库获取用户别名
        string userAlias = "jane_smith";

        var parameters = new Dictionary<string, string>
        {
            { "UserAlias", userAlias }
        };

        bool isEnabled = await _featureManager.IsEnabledAsync("YourFeatureName", parameters);

        if (isEnabled)
        {
            // 执行功能启用后的业务逻辑
        }

        _appLifetime.StopApplication();
    }

    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}

注意事项 #

• 确保过滤器的构造函数中IHttpContextAccessor是可选的（设置默认值null），这样在非Web场景下也能正常实例化。
• 如果使用强类型参数传递，记得要确保FeatureFilterEvaluationContext.Parameters能正确反序列化对象，使用AddJson扩展方法是最简单的方式。
• App Configuration中仍然需要配置过滤器的固定参数（比如AllowedUsers的Aliases值），手动传递的是运行时的动态参数（比如当前用户别名）。

内容的提问来源于stack exchange，提问作者PraveenLearnsEveryday