.NET MAUI中为Azure B2C多用户流配置多IPublicClientApplication实例的正确方法

.NET MAUI使用的Microsoft.Extensions.DependencyInjection容器中，同一服务类型的多次注册会被最后一次注册覆盖。你两次注册IPublicClientApplication类型，最终所有依赖该类型的服务都会拿到最后注册的密码重置实例，这就是两个认证服务共用同一实例的根本原因。

下面提供三种可行的解决方式，按简洁度和推荐度排序：

方案1：直接在服务注册时传入实例（最简洁） #

不需要修改现有认证服务的代码，直接在注册服务时创建对应IPublicClientApplication实例并传入构造函数：

// 创建登录策略对应的实例
var signInApp = PublicClientApplicationBuilder
    .Create(Constants.ClientId)
    .WithIosKeychainSecurityGroup(Constants.IosKeychainSecurityGroups)
    .WithRedirectUri($"msal{Constants.ClientId}://auth")
    .WithB2CAuthority(Constants.AuthoritySignIn)
    .Build();
// 注册登录服务，直接传入实例
mauiAppBuilder.Services.AddScoped<IAuthService>(sp => new AuthServiceB2CSignInSignUp(signInApp));

// 创建密码重置策略对应的实例
var resetPasswordApp = PublicClientApplicationBuilder
    .Create(Constants.ClientId)
    .WithIosKeychainSecurityGroup(Constants.IosKeychainSecurityGroups)
    .WithRedirectUri($"msal{Constants.ClientId}://auth")
    .WithB2CAuthority(Constants.AuthorityPasswordReset)
    .Build();
// 注册密码重置服务，直接传入实例
mauiAppBuilder.Services.AddScoped<IAuthServiceB2CResetPassword>(sp => new AuthServiceB2CResetPassword(resetPasswordApp));

方案2：使用Keyed Services（.NET 6+官方推荐） #

利用.NET 6引入的Keyed Services特性，为不同实例指定唯一标识，在注入时通过标识区分：

步骤1：修改服务注册 #

// 注册登录用的IPublicClientApplication，指定键为"SignIn"
mauiAppBuilder.Services.AddKeyedScoped<IPublicClientApplication>("SignIn", sp =>
{
    return PublicClientApplicationBuilder
        .Create(Constants.ClientId)
        .WithIosKeychainSecurityGroup(Constants.IosKeychainSecurityGroups)
        .WithRedirectUri($"msal{Constants.ClientId}://auth")
        .WithB2CAuthority(Constants.AuthoritySignIn)
        .Build();
});

// 注册密码重置用的IPublicClientApplication，指定键为"ResetPassword"
mauiAppBuilder.Services.AddKeyedScoped<IPublicClientApplication>("ResetPassword", sp =>
{
    return PublicClientApplicationBuilder
        .Create(Constants.ClientId)
        .WithIosKeychainSecurityGroup(Constants.IosKeychainSecurityGroups)
        .WithRedirectUri($"msal{Constants.ClientId}://auth")
        .WithB2CAuthority(Constants.AuthorityPasswordReset)
        .Build();
});

// 正常注册认证服务
mauiAppBuilder.Services.AddScoped<IAuthService, AuthServiceB2CSignInSignUp>();
mauiAppBuilder.Services.AddScoped<IAuthServiceB2CResetPassword, AuthServiceB2CResetPassword>();

步骤2：修改认证服务构造函数 #

通过[FromKeyedServices]属性指定要注入的实例标识：

// 登录服务构造函数
public class AuthServiceB2CSignInSignUp : IAuthService
{
    private readonly IPublicClientApplication _signInApp;

    public AuthServiceB2CSignInSignUp([FromKeyedServices("SignIn")] IPublicClientApplication signInApp)
    {
        _signInApp = signInApp;
    }

    // 原有方法保持不变
}

// 密码重置服务构造函数
public class AuthServiceB2CResetPassword : IAuthServiceB2CResetPassword
{
    private readonly IPublicClientApplication _resetApp;

    public AuthServiceB2CResetPassword([FromKeyedServices("ResetPassword")] IPublicClientApplication resetApp)
    {
        _resetApp = resetApp;
    }

    // 原有方法保持不变
}

方案3：创建包装类区分实例（兼容旧版本） #

如果需要兼容.NET 6以下版本，可以创建专属包装类来区分不同的IPublicClientApplication实例：

步骤1：创建包装类 #

// 登录策略专用包装类
public class SignInPublicClientApplication : IPublicClientApplication
{
    private readonly IPublicClientApplication _innerApp;

    public SignInPublicClientApplication(IPublicClientApplication innerApp)
    {
        _innerApp = innerApp;
    }

    // 实现IPublicClientApplication的所有接口方法，直接委托给_innerApp
    public Task<IEnumerable<IAccount>> GetAccountsAsync(string? policy = null)
        => _innerApp.GetAccountsAsync(policy);

    public AcquireTokenInteractiveParameterBuilder AcquireTokenInteractive(IEnumerable<string> scopes)
        => _innerApp.AcquireTokenInteractive(scopes);

    // 其他接口方法同理，全部委托给_innerApp
}

// 密码重置策略专用包装类
public class ResetPasswordPublicClientApplication : IPublicClientApplication
{
    private readonly IPublicClientApplication _innerApp;

    public ResetPasswordPublicClientApplication(IPublicClientApplication innerApp)
    {
        _innerApp = innerApp;
    }

    // 同样实现所有IPublicClientApplication接口方法，委托给_innerApp
}

步骤2：修改服务注册 #

// 注册登录用的包装实例
mauiAppBuilder.Services.AddScoped<SignInPublicClientApplication>(sp =>
{
    var app = PublicClientApplicationBuilder
        .Create(Constants.ClientId)
        .WithIosKeychainSecurityGroup(Constants.IosKeychainSecurityGroups)
        .WithRedirectUri($"msal{Constants.ClientId}://auth")
        .WithB2CAuthority(Constants.AuthoritySignIn)
        .Build();
    return new SignInPublicClientApplication(app);
});

// 注册密码重置用的包装实例
mauiAppBuilder.Services.AddScoped<ResetPasswordPublicClientApplication>(sp =>
{
    var app = PublicClientApplicationBuilder
        .Create(Constants.ClientId)
        .WithIosKeychainSecurityGroup(Constants.IosKeychainSecurityGroups)
        .WithRedirectUri($"msal{Constants.ClientId}://auth")
        .WithB2CAuthority(Constants.AuthorityPasswordReset)
        .Build();
    return new ResetPasswordPublicClientApplication(app);
});

// 注册认证服务
mauiAppBuilder.Services.AddScoped<IAuthService, AuthServiceB2CSignInSignUp>();
mauiAppBuilder.Services.AddScoped<IAuthServiceB2CResetPassword, AuthServiceB2CResetPassword>();

步骤3：修改认证服务构造函数 #

注入对应的包装类：

// 登录服务构造函数
public class AuthServiceB2CSignInSignUp : IAuthService
{
    private readonly IPublicClientApplication _signInApp;

    public AuthServiceB2CSignInSignUp(SignInPublicClientApplication signInApp)
    {
        _signInApp = signInApp;
    }

    // 原有方法保持不变
}

// 密码重置服务构造函数
public class AuthServiceB2CResetPassword : IAuthServiceB2CResetPassword
{
    private readonly IPublicClientApplication _resetApp;

    public AuthServiceB2CResetPassword(ResetPasswordPublicClientApplication resetApp)
    {
        _resetApp = resetApp;
    }

    // 原有方法保持不变
}

内容的提问来源于stack exchange，提问作者Vladimir