How can Unity's dependency injection handle conditional authentication based on provider selection?

Conditional Dependency Resolving in Unity

In this article, we'll delve into the concept of conditional dependency resolving in Unity, addressing the implementation of conditional authentication based on the provided code sample.

Conditional Resolving

Conditional resolving enables you to construct objects based on specific conditions. In our case, we want Unity to select the appropriate authentication provider (Twitter or Facebook) based on the user's authentication method.

Interfaces

To achieve this, we define an IAuthenticate interface with an AppliesTo method that tracks which authentication method is supported by a specific provider.

public interface IAuthenticate{
    bool Login(string user, string pass);
    bool AppliesTo(string providerName);
}

Authenticate Providers

For each authentication provider (Twitter and Facebook), we implement the IAuthenticate interface and override the AppliesTo method to specify if it handles the specified authentication method.

public class TwitterAuth : IAuthenticate {
    ...
    bool AppliesTo(string providerName) {
        // Check if this class name matches the provider name
    }
}

Strategy

We create an IAuthenticateStrategy interface that serves as a central point for performing authentication. This strategy includes a method for selecting the appropriate provider based on the providerName.

public interface IAuthenticateStrategy{
    bool Login(string providerName, string user, string pass);
}

Unity Registration

In our Unity configuration, we register the authentication providers and the strategy instance.

unityContainer.RegisterType<IAuthenticate, TwitterAuth>("twitterAuth");
unityContainer.RegisterType<IAuthenticate, FacebookAuth>("facebookAuth");
unityContainer.RegisterType<IAuthenticateStrategy, AuthenticateStrategy>(
    // Resolve authentication providers array
    new InjectionConstructor(new ResolvedArrayParameter<IAuthenticate>(
        new ResolvedParameter<IAuthenticate>("twitterAuth"),
        new ResolvedParameter<IAuthenticate>("facebookAuth")
    ))
);

Usage

The authenticate controller is now modified to use the strategy interface.

private readonly IAuthenticateStrategy _authenticateStrategy;

public AuthenticateController(IAuthenticateStrategy authenticateStrategy) {...}

public virtual ActionResult Twitter(string user, string pass) {...}

public virtual ActionResult Facebook(string user, string pass) {...}

Now, when the Login action is invoked with a specific provider name, the strategy will pick the correct authentication provider and perform the login accordingly.

Improved Design

The strategy pattern divides the authentication handling from the controller logic. This allows for easier maintenance and extensibility by simply adding new authentication providers without modifying the controller code.

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