若要在非web.sdk项目中使用ASP.NET Core 3+类型，请使用共享框架引用。
示例项目：

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFrameworks>net6.0</TargetFrameworks>
    <Nullable>enable</Nullable>
    <OutputType>Library</OutputType>
  </PropertyGroup>

  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
  </ItemGroup>

</Project>

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然而，请注意，这主要是为了提供具有端点等的库。在业务层中使用此引用将业务逻辑与Web API框架耦合。
更灵活的方法是在业务逻辑项目中为所需的功能提供接口，并在API项目中提供实现。
举个例子

// In business project
public interface IMySpecialContext
{
    string Value { get; }
}

// In API project
public class HttpMySpecialContext : IMySpecialContext
{
    private readonly IHttpContextAccessor _httpContextAccessor;

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

    public string Value
    {
        // Probably should throw for missing HttpContext or header.
        get => _httpContextAccessor.HttpContext?.Request.Headers["X-My-Special-Header"]!;
    }
}

// In unit tests
public class DummyMySpecialContext : IMySpecialContext
{
    public string Value => "Dummy Special Context Value";
}