# 2.4: Registering Auth Service

We need to make our `AuthService.cs` class injectable into other parts of our application.

Open up the `Startup` class in the `.API` project.

Remember the `ConfigureServices()` method? This is where we register services for dependency injection.

```csharp
public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<EFConnectContext>(x => x.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
    services.AddMvc();
    services.AddScoped<IAuthService, AuthService>();      // registering our AuthService
}
```

The formula is:

`service.[Lifetime]<[interface], [concrete]>();`

## Transient vs. Singleton vs. Scoped

What is the `AddScoped()` method?

There are three different "lifetimes" we have to choose from for dependency injection.

1. **Transient** - each time the service is requested, a new instance of our service is created.
2. **Scoped** - one instance of our service is created for each web request.
3. **Singleton** - one instance of our service is created for the entire lifetime of our application. After initial request is made - all additional requests will use the same instance.

These are a bit confusing, but they will make more sense as we use them.

**Note:** built-in methods like `AddDbContext()` and `AddMvc()` handle it for us. This is just for custom services we want to inject.