Dependency injection in requirement handlers in ASP.NET Core

Authorization handlers must be registered in the service collection during configuration using dependency injection.

Suppose you had a repository of rules you wanted to evaluate inside an authorization handler and that repository was registered in the service collection. Authorization resolves and injects that into the constructor.

For example, to use ASP.NET's logging infrastructure, inject ILoggerFactory into the handler. Such a handler might look like the following code:

public class LoggingAuthorizationHandler : AuthorizationHandler<MyRequirement>
   {
       ILogger _logger;

       public LoggingAuthorizationHandler(ILoggerFactory loggerFactory)
       {
           _logger = loggerFactory.CreateLogger(this.GetType().FullName);
       }

       protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, MyRequirement requirement)
       {
           _logger.LogInformation("Inside my handler");
           // Check if the requirement is fulfilled.
           return Task.CompletedTask;
       }
   }

The preceding handler can be registered with any service lifetime. The following code uses AddSingleton to register the preceding handler:

services.AddSingleton<IAuthorizationHandler, LoggingAuthorizationHandler>();

An instance of the handler is created when the app starts, and DI injects the registered ILoggerFactory into the constructor.

Note

Handlers that use Entity Framework shouldn't be registered as singletons.