Blazor API项目中ILoggerProvider如何获取用户名？

我想要构建自定义ILoggerProvider，使其具备获取用户名的功能，该如何实现？我使用外部OIDC服务，在API中已配置如下认证代码：

builder.Services
.AddAuthentication("Bearer")
.AddJwtBearer("Bearer", options =>
{
    options.Authority = "https://xxxx/auth/realms/dev";
    options.TokenValidationParameters.ValidateAudience = false;
});

同时已注册自定义DbLoggerProvider：

builder.Services.AddScoped<ILoggerProvider,DbLoggerProvider>();

当我在DbLoggerProvider的构造函数中注入AuthenticationStateProvider时，构建时出现报错：

System.AggregateException
 Message=Some services are not able to be constructed
 Source=Microsoft.Extensions.DependencyInjection
 StackTrace:
 at
 Microsoft.Extensions.DependencyInjection.ServiceProvider. .ctor(ICollection`1 serviceDescriptors, ServiceProviderOptions options)
at 
Microsoft.Extensions.DependencyInjection.ServiceCollection 
ContainerBuilderExtensions.BuildServiceProvider 
(IServiceCollection services, ServiceProviderOptions options)
at Microsoft.Extensions.Hosting.HostApplicationBuilder.Build()
at Microsoft.AspNetCore.Builder.WebApplicationBuilder.Build()
at Program.<Main>$(String[] args) in D:\x\Server\Program.cs:line 
153
This exception was originally thrown at this call stack:
[External Code]
Inner Exception 1:
InvalidOperationException: Error while validating the service 
descriptor 'ServiceType: Microsoft.Extensions.Hosting.IHostApplicationLifetime Lifetime: Singleton ImplementationType: Microsoft.Extensions.Hosting.Internal.ApplicationLifetime': Unable to resolve service for type 'Microsoft.AspNetCore.Components.Authorization.AuthenticationStateProvider' while attempting to activate 'x.Server.Core.Providers.DbLoggerProvider'.
Inner Exception 2:
InvalidOperationException: Unable to resolve service for type 
'Microsoft.AspNetCore.Components.Authorization. 
AuthenticationStateProvider' while attempting to activate 
'x.Server.Core.Providers.DbLoggerProvider'.

在控制器中我通过以下代码获取用户名：

string login = User.Claims.Where(p => p.Type == "preferred_username").First().Value;

请问如何在LoggerProvider中获取该用户名？另外，控制器并非通过AuthenticationStateProvider获取用户对象，它是如何实现的？

一、在自定义ILoggerProvider中获取用户名的正确方式 #

你遇到的注入报错是因为AuthenticationStateProvider是Blazor专用服务，纯ASP.NET Core API场景下不会默认注册；且ILoggerProvider的生命周期是Singleton（即便你注册成Scoped，框架内部也会按Singleton处理），而用户上下文是请求级的（Scoped），直接在Provider构造函数注入请求级服务会导致生命周期冲突。

正确的做法是在自定义Logger（而非LoggerProvider）中通过IHttpContextAccessor获取当前请求的用户上下文，步骤如下：

1. 注册IHttpContextAccessor服务：

builder.Services.AddHttpContextAccessor();

2. 修改自定义DbLoggerProvider，在创建Logger实例时传入IHttpContextAccessor：

public class DbLoggerProvider : ILoggerProvider
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public DbLoggerProvider(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public ILogger CreateLogger(string categoryName)
    {
        return new DbLogger(_httpContextAccessor);
    }

    public void Dispose() { }
}

3. 在自定义DbLogger中获取用户名：

public class DbLogger : ILogger
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public DbLogger(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public IDisposable BeginScope<TState>(TState state) => null;

    public bool IsEnabled(LogLevel logLevel) => true;

    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
    {
        // 获取当前请求的用户名，无用户时返回"匿名用户"
        var userName = _httpContextAccessor.HttpContext?.User?.Claims
            .FirstOrDefault(c => c.Type == "preferred_username")?.Value ?? "匿名用户";

        // 后续执行写入数据库的逻辑，带上userName即可
        // ...
    }
}

4. 按框架规范将LoggerProvider注册为Singleton：

builder.Services.AddSingleton<ILoggerProvider, DbLoggerProvider>();

二、控制器中获取用户对象的原理 #

控制器中的User属性是ASP.NET Core框架自动注入的，本质是直接读取当前请求的HttpContext.User：

• 配置JWT认证后，认证中间件会在请求到达时解析Bearer令牌，将令牌中的声明信息解析到HttpContext.User中。
• 控制器基类（ControllerBase）内置了HttpContext属性，可直接访问User；而AuthenticationStateProvider是Blazor场景下专门处理组件用户状态的服务，和API控制器的用户获取逻辑完全无关。

内容的提问来源于stack exchange，提问作者Dorian