HTTP認證之基本認證——Basic（二）

xiaoxiaotank發表於2019-06-13

在HTTP認證之基本認證——Basic（一）中介紹了Basic認證的工作原理和流程，接下來就趕緊通過程式碼來實踐一下，以下教程基於ASP.NET Core WebApi框架。如有興趣，可檢視原始碼

一、準備工作

在開始之前，先把最基本的使用者名稱密碼校驗邏輯準備好，只有一個認證方法：

public class UserService
{
    public static User Authenticate(string userName, string password)
    {
        //使用者名稱、密碼不為空且相等時認證成功
        if (!string.IsNullOrEmpty(userName) 
            && !string.IsNullOrEmpty(password) 
            && userName == password)
        {
            return new User()
            {
                UserName = userName,
                Password = password
            };
        }

        return null;
    }
}

public class User
{
    public string UserName { get; set; }
    public string Password { get; set; }
}

二、編碼

1.首先，先確定使用的認證方案為Basic，並提供預設的的Realm，

public const string AuthenticationScheme = "Basic";
public const string AuthenticationRealm = "Test Realm";

2.然後，解析HTTP Request獲取到Authorization標頭

private string GetCredentials(HttpRequest request)
{
    string credentials = null;

    string authorization = request.Headers[HeaderNames.Authorization];
    //請求中存在 Authorization 標頭且認證方式為 Basic
    if (authorization?.StartsWith(AuthenticationScheme, StringComparison.OrdinalIgnoreCase) == true)
    {
        credentials = authorization.Substring(AuthenticationScheme.Length).Trim();
    }
   
    return credentials;
}

3.接著通過Base64逆向解碼，得到要認證的使用者名稱和密碼。如果認證失敗，則返回401 Unauthorized（不推薦返回403 Forbidden，因為這會導致使用者在不重新整理頁面的情況下無法重新嘗試認證）；如果認證成功，繼續處理請求。

public class AuthorizationFilterAttribute : Attribute, IAuthorizationFilter
{
    public void OnAuthorization(AuthorizationFilterContext context)
    {
        //請求允許匿名訪問
        if (context.Filters.Any(item => item is IAllowAnonymousFilter)) return;

        var credentials = GetCredentials(context.HttpContext.Request);
        //已獲取到憑證
        if(credentials != null)
        {
            try
            {
                //Base64逆向解碼得到使用者名稱和密碼
                credentials = Encoding.UTF8.GetString(Convert.FromBase64String(credentials));
                var data = credentials.Split(':');
                if (data.Length == 2)
                {
                    var userName = data[0];
                    var password = data[1];
                    var user = UserService.Authenticate(userName, password);
                    //認證成功
                    if (user != null) return;
                }
            }
            catch { }
        }

        //認證失敗返回401
        context.Result = new UnauthorizedResult();
        //新增質詢
        AddChallenge(context.HttpContext.Response); 
    }
    
    private void AddChallenge(HttpResponse response)
        => response.Headers.Append(HeaderNames.WWWAuthenticate, $"{ AuthenticationScheme } Realm={ AuthenticationRealm }");
}

4.最後，在需要認證的Action上加上過濾器[AuthorizationFilter]，大功告成！自己測試一下吧

三、封裝為中介軟體

ASP.NET Core相比ASP.NET最大的突破大概就是外掛配置化了——通過將各個功能封裝成中介軟體，應用AOP的設計思想配置到應用程式中。以下封裝採用Jwt Bearer封裝規範。

首先封裝常量

public static class BasicDefaults
{
    public const string AuthenticationScheme = "Basic";
}

2.然後封裝Basic認證的Options，包括Realm和事件，繼承自Microsoft.AspNetCore.Authentication.AuthenticationSchemeOptions。在事件內部，我們定義了認證行為和質詢行為，分別用來校驗認證是否通過和在HTTP Response中新增質詢資訊。我們將認證邏輯封裝成一個委託，與認證行為獨立開來，方便使用者使用委託自定義認證規則。

public class BasicOptions : AuthenticationSchemeOptions
{
    public string Realm { get; set; }
    public new BasicEvents Events
    {
        get => (BasicEvents)base.Events; 
        set => base.Events = value; 
    }
}

public class BasicEvents
{
    public Func<ValidateCredentialsContext, Task> OnValidateCredentials { get; set; } = context => Task.CompletedTask;

    public Func<BasicChallengeContext, Task> OnChallenge { get; set; } = context => Task.CompletedTask;

    public virtual Task ValidateCredentials(ValidateCredentialsContext context) => OnValidateCredentials(context);

    public virtual Task Challenge(BasicChallengeContext context) => OnChallenge(context);
}

/// <summary>
/// 封裝認證引數資訊上下文
/// </summary>
public class ValidateCredentialsContext : ResultContext<BasicAuthenticationOptions>
{
    public ValidateCredentialsContext(HttpContext context, AuthenticationScheme scheme, BasicAuthenticationOptions options) : base(context, scheme, options)
    {
    }
    
    public string UserName { get; set; }
    public string Password { get; set; }
}

public class BasicChallengeContext : PropertiesContext<BasicOptions>
{
    public BasicChallengeContext(
        HttpContext context,
        AuthenticationScheme scheme,
        BasicOptions options,
        AuthenticationProperties properties)
        : base(context, scheme, options, properties)         
    {
    }
    
    /// <summary>
    /// 在認證期間出現的異常
    /// </summary>
    public Exception AuthenticateFailure { get; set; }

    /// <summary>
    /// 指定是否已被處理，如果已處理，則跳過預設認證邏輯
    /// </summary>
    public bool Handled { get; private set; }

    /// <summary>
    /// 跳過預設認證邏輯
    /// </summary>
    public void HandleResponse() => Handled = true;
}

3.接下來，就是對認證過程處理的封裝了，需要繼承自Microsoft.AspNetCore.Authentication.AuthenticationHandler

public class BasicHandler : AuthenticationHandler<BasicOptions>
{
    public BasicHandler(IOptionsMonitor<BasicOptions> options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock) : base(options, logger, encoder, clock)
    {
    }

    protected new BasicEvents Events
    {
        get => (BasicEvents)base.Events; 
        set => base.Events = value; 
    }
    
    /// <summary>
    /// 確保建立的 Event 型別是 BasicEvents
    /// </summary>
    /// <returns></returns>    
    protected override Task<object> CreateEventsAsync() => Task.FromResult<object>(new BasicEvents());

    protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        var credentials = GetCredentials(Request);
        if(credentials == null)
        {
            return AuthenticateResult.NoResult();
        }

        try
        {
            credentials = Encoding.UTF8.GetString(Convert.FromBase64String(credentials));
            var data = credentials.Split(':');
            if(data.Length != 2)
            {
                return AuthenticateResult.Fail("Invalid credentials, error format.");
            }

           var validateCredentialsContext = new ValidateCredentialsContext(Context, Scheme, Options)
            {
                UserName = data[0],
                Password = data[1]
            };
            await Events.ValidateCredentials(validateCredentialsContext);

            //認證通過
            if(validateCredentialsContext.Result?.Succeeded == true)
            {
                var ticket = new AuthenticationTicket(validateCredentialsContext.Principal, Scheme.Name);
                return AuthenticateResult.Success(ticket);
            }

            return AuthenticateResult.NoResult();
        }
        catch(FormatException)
        {
            return AuthenticateResult.Fail("Invalid credentials, error format.");
        }
        catch(Exception ex)
        {
            return AuthenticateResult.Fail(ex.Message);
        }
    }

    protected override async Task HandleChallengeAsync(AuthenticationProperties properties)
    {
        var authResult = await HandleAuthenticateOnceSafeAsync();
        var challengeContext = new BasicChallengeContext(Context, Scheme, Options, properties)
        {
            AuthenticateFailure = authResult?.Failure
        };
        await Events.Challenge(challengeContext);
        //質詢已處理
        if (challengeContext.Handled) return;
    
        var challengeValue = $"{ BasicDefaults.AuthenticationScheme } realm={ Options.Realm }";
        var error = challengeContext.AuthenticateFailure?.Message;
        if(string.IsNullOrWhiteSpace(error))
        {
            //將錯誤資訊封裝到內部
            challengeValue += $" error={ error }";
        }
    
        Response.StatusCode = (int)HttpStatusCode.Unauthorized;
        Response.Headers.Append(HeaderNames.WWWAuthenticate, challengeValue);
    }

    private string GetCredentials(HttpRequest request)
    {
        string credentials = null;

        string authorization = request.Headers[HeaderNames.Authorization];
        //存在 Authorization 標頭
        if (authorization != null)
        {
            var scheme = BasicDefaults.AuthenticationScheme;
            if (authorization.StartsWith(scheme, StringComparison.OrdinalIgnoreCase))
            {
                credentials = authorization.Substring(scheme.Length).Trim();
            }
        }

        return credentials;
    }
}

4.最後，就是要把封裝的介面暴露給使用者了，這裡使用擴充套件方法的形式，雖然有4個方法，但實際上都是過載，是同一種行為。

public static class BasicExtensions
{
    public static AuthenticationBuilder AddBasic(this AuthenticationBuilder builder)
        => builder.AddBasic(BasicDefaults.AuthenticationScheme, _ => { });

    public static AuthenticationBuilder AddBasic(this AuthenticationBuilder builder, Action<BasicOptions> configureOptions)
        => builder.AddBasic(BasicDefaults.AuthenticationScheme, configureOptions);

    public static AuthenticationBuilder AddBasic(this AuthenticationBuilder builder, string authenticationScheme, Action<BasicOptions> configureOptions)
        => builder.AddBasic(authenticationScheme, displayName: null, configureOptions: configureOptions);

    public static AuthenticationBuilder AddBasic(this AuthenticationBuilder builder, string authenticationScheme, string displayName, Action<BasicOptions> configureOptions)
        => builder.AddScheme<BasicOptions, BasicHandler>(authenticationScheme, displayName, configureOptions);
}

5.Basic認證庫已經封裝好了，我們建立一個ASP.NET Core WebApi程式來測試一下吧。

//在 ConfigureServices 中配置認證中介軟體
public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(BasicDefaults.AuthenticationScheme)
        .AddBasic(options =>
        {
            options.Realm = "Test Realm";   
            options.Events = new BasicEvents
            {
                OnValidateCredentials = context =>
                {
                    var user = UserService.Authenticate(context.UserName, context.Password);
                    if (user != null)
                    {
                        //將使用者資訊封裝到HttpContext
                        var claim = new Claim(ClaimTypes.Name, context.UserName);
                        var identity = new ClaimsIdentity(BasicDefaults.AuthenticationScheme);
                        identity.AddClaim(claim);

                        context.Principal = new ClaimsPrincipal(identity);
                        context.Success();
                    }
                    return Task.CompletedTask;
                }
            };
        });
}

//在 Configure 中啟用認證中介軟體
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseAuthentication();
}

對了，一定要記得為需要認證的Action新增[Authorize]特性，否則前面做的一切都是徒勞+_+

檢視原始碼

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HTTP認證之基本認證——Basic（二）

一、準備工作

二、編碼

三、封裝為中介軟體

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