.Net Core Api - 基于请求值的自定义 JSON 解析器

我希望拥有一切OkObjectResult来自我的 api 的响应通过我拥有的自定义 JSON 解析器运行。解析器依赖于一些特定于请求的数据——即用户的角色。它实际上类似于控制器上的 Authorize 属性，但用于从 API 传递到 UI 的数据传输对象。

我可以通过 AddJsonOptions 在配置服务中添加解析器，但它无法访问那里的用户信息。

如何将基于请求的值传递给该解析器？我是在寻找某种自定义中间件，还是其他什么？

作为示例，如果我有一个带有一些自定义属性装饰器的对象，如下所示：

public class TestObject
{
    public String Field1 => "NoRestrictions";
    [RequireRoleView("Admin")]
    public String Field2 => "ViewRequiresAdmin";
}

并使用不同的角色调用我的自定义序列化器，如下所示：

var test = new TestObject();
var userRoles = GetRoles(); // "User" for the sake of this example
var outputJson = JsonConvert.SerializeObject(test, 
                    new JsonSerializerSettings { 
                        ContractResolver = new MyCustomResolver(userRoles) 
                    });

然后输出 JSON 将跳过用户无法访问的任何内容，如下所示：

{
    "Field1":"NoRestrictions",
    // Note the absence of Field2, since it has [RequireRoleView("Admin")]
}

假设你有一个自定义RequireRoleViewAttribute:

[AttributeUsageAttribute(AttributeTargets.All, Inherited = true, AllowMultiple = true)]
public class RequireRoleViewAttribute : Attribute
{
    
    public string Role;

    public RequireRoleViewAttribute(string role){
        this.Role = role;
    }
}

如何将基于请求的值传递给该解析器？

你可以有一个IServiceProvider注入您的自定义解析器：

public class RoleBasedContractResolver : DefaultContractResolver
{
    public IServiceProvider ServiceProvider { get; }
    public RoleBasedContractResolver( IServiceProvider sp)
    {
        this.ServiceProvider = sp;
    }
    
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var contextAccessor = this.ServiceProvider.GetRequiredService<IHttpContextAccessor>() ;
        var context = contextAccessor.HttpContext;
        var user = context.User;
        
       // if you're using the Identity, you can get the userManager :
       var userManager = context.RequestServices.GetRequiredService<UserManager<IdentityUser>>();

       // ...
    }
}

这样我们就可以得到HttpContext and User如我们所愿。如果您使用身份，您还可以获得UserManager服务和角色。

现在我们可以跟随@dbc的建议 https://stackoverflow.com/users/3744182/dbc来控制ShouldSerialize https://www.newtonsoft.com/json/help/html/ConditionalProperties.htm:

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var contextAccessor = this.ServiceProvider.GetRequiredService<IHttpContextAccessor>() ;
        var context = contextAccessor.HttpContext;
        var user = context.User;

        // if you use the Identitiy, you can get the usermanager
        //UserManager<IdentityUser> 
        var userManager = context.RequestServices.GetRequiredService<UserManager<IdentityUser>>();

        JsonProperty property = base.CreateProperty(member, memberSerialization);

        // get the attributes
        var attrs=member.GetCustomAttributes<RequireRoleViewAttribute>();
        
        // if no [RequireResoveView] decorated, always serialize it
        if(attrs.Count()==0) {
            property.ShouldDeserialize = instance => true;
            return property;
        }

        // custom your logic to dertermine wether should serialize the property
        // I just use check if it can statisify any the condition :
        var roles = this.GetIdentityUserRolesAsync(context,userManager).Result;
        property.ShouldSerialize = instance => {
            var resource = new { /* any you need  */ };
            return attrs.Any(attr => {
                var rolename = attr.Role;
                return roles.Any(r => r == rolename ) ;
            }) ? true : false;
        };
        return property;
    }

功能GetIdentityUserRolesAsync这是使用当前检索角色的辅助方法HttpContext和UserManger服务 ：

private async Task<IList<string>> GetIdentityUserRolesAsync(HttpContext context, UserManager<IdentityUser> userManager)
{
    var rolesCached= context.Items["__userRoles__"];
    if( rolesCached != null){
        return (IList<string>) rolesCached;
    }
    var identityUser = await userManager.GetUserAsync(context.User);
    var roles = await userManager.GetRolesAsync(identityUser);
    context.Items["__userRoles__"] = roles;
    return roles;
}

如何注射IServiceProvider详细信息：

技巧在于如何配置默认值MvcJwtOptions与IServiceProvider.

不要配置JsonOptions by :

services.AddMvc().
    .AddJsonOptions(o =>{
        // o. 
    });

因为它不允许我们添加IServiceProvider范围。

我们可以自定义一个子类MvcJsonOptions:

// in .NET 3.1 and above, change this from MvcJsonOptions to MvcNewtonsoftJsonOptions
public class MyMvcJsonOptionsWrapper : IConfigureOptions<MvcJsonOptions>
{
    IServiceProvider ServiceProvider;
    public MyMvcJsonOptionsWrapper(IServiceProvider serviceProvider)
    {
        this.ServiceProvider = serviceProvider;
    }
    public void Configure(MvcJsonOptions options)
    {
        options.SerializerSettings.ContractResolver =new RoleBasedContractResolver(ServiceProvider);
    }
}

并通过以下方式注册服务：

services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();

// don't forget to add the IHttpContextAccessor
// in .NET 3.1 and above, change this from MvcJsonOptions to MvcNewtonsoftJsonOptions
services.AddTransient<IConfigureOptions<MvcJsonOptions>,MyMvcJsonOptionsWrapper>();
    

测试用例 ：

假设您有一个自定义 POCO ：

public class TestObject
{
    public string Field1 => "NoRestrictions";

    [RequireRoleView("Admin")]
    public string Field2 => "ViewRequiresAdmin";

    [RequireRoleView("HR"),RequireRoleView("OP")]
    public string Field3 => "ViewRequiresHROrOP";

    [RequireRoleView("IT"), RequireRoleView("HR")]
    public string Field4 => "ViewRequiresITOrHR";

    [RequireRoleView("IT"), RequireRoleView("OP")]
    public string Field5 => "ViewRequiresITOrOP";
}

当前用户具有以下角色：Admin and HR:

结果将是：

{"Field1":"NoRestrictions","Field2":"ViewRequiresAdmin","Field3":"ViewRequiresHROrOP","Field4":"ViewRequiresITOrHR"}

使用操作方法进行测试的屏幕截图：