Authorization In Asp.NetPart IV

Resource Based Authorization

Today we will be discussing resource based authorization.

Often authorization is based upon the accessed resource . E.g. a document might have an author property. So only the author would be allowed to update it; the resource must be loaded from the document repository before an authorization access can be made. This can't be done with an Authorize attribute, as feature evaluation takes place before data binding and before the code to load a resource runs inside an action. Instead of the declarative authorization, the attribute method, we must use impervious authorization, where a developer calls upon an authorize function within his own code.

Authorizing within a code

Authorization is executed as a service, IAuthorizationService, registered in the service collection and available via dependency injection for Controllers to approach.

public class DocumentController : Controller

{

IAuthorizationService _authorizationService;

public DocumentController(IAuthorizationService authorizationService)

{

_authorizationService = authorizationService;

}

}

IAuthorizationService has 2 methods: in one, you pass the resource and the policy name and in the other, you pass the resource and a list of requirements to assess.

Task<bool> AuthorizeAsync(ClaimsPrincipal user,

object resource,

IEnumerable<IAuthorizationRequirement> requirements);

Task<bool> AuthorizeAsync(ClaimsPrincipal user,

object resource,

string policyName);

To call upon the service load resource within action then call the AuthorizeAsync overload you require. e.g.

public async Task<IActionResult> Edit(Guid documentId)

{

Document document = documentRepository.Find(documentId);

if (document == null)

{

return new HttpNotFoundResult();

}

if (await authorizationService.AuthorizeAsync(User, document, "EditPolicy"))

{

return View(document);

}

else

{

return new ChallengeResult();

}

}

Writing a resource based handler

Now to write a handler for resource based authorization is not very much different to write a plain requirements handler. You create a requirement, and then execute a handler for the requirement, then specify the requirement as before and also the resource type.

Therefore, a handler which might accept a Document resource would look as below:

public class DocumentAuthorizationHandler : AuthorizationHandler<MyRequirement, Document>

{

public override Task HandleRequirementAsync(AuthorizationHandlerContext context,

MyRequirement requirement,

Document resource)

{

// Ratify the requirement against the resource and identity.

return Task.CompletedTask;

}

}

Don’t forget you also need to list your handler in the ConfigureServices method;

services.AddSingleton<IAuthorizationHandler, DocumentAuthorizationHandler>();

Requirements

If you want to make decisions based on operations such as read, write, update and delete, you can use the OperationAuthorizationRequirement in the Microsoft.AspNetCore.Authorization.Infrastructure namespace. This previously built requirement class helps you to write a single handler which has a set parameterized operation name, rather than develop individual classes for each operation. To utilize it provide some operation names:

public static class Operations

{

public static OperationAuthorizationRequirement Create =

new OperationAuthorizationRequirement { Name = "Create" };

public static OperationAuthorizationRequirement Read =

new OperationAuthorizationRequirement { Name = "Read" };

public static OperationAuthorizationRequirement Update =

new OperationAuthorizationRequirement { Name = "Update" };

public static OperationAuthorizationRequirement Delete =

new OperationAuthorizationRequirement { Name = "Delete" };

}

Your handler could then be executed as follows, using a hypothetical Document class as the resource;

public class DocumentAuthorizationHandler :

AuthorizationHandler<OperationAuthorizationRequirement, Document>

{

public override Task HandleRequirementAsync(AuthorizationHandlerContext

OperationAuthorizationRequirement ,

Document resource)

{

// Validate the operation using the resource, the identity and

// the Name property value from the requirement.

return Task.CompletedTask;

}

}

You can view the handler works upon OperationAuthorizationRequirement. The code inside the handler must take the Name property of the supplied need into account when making its evaluations.

To call an operational resource handler you are required to specify the operation when calling AuthorizeAsync in your action. For example

if (await authorizationService.AuthorizeAsync(User, document, Operations.Read))

{

return View(document);

}

else

{

return new ChallengeResult();

}

This example checks if the user is able to perform the read function for the current document. If authorization succeeds the view for the document will be returned.

If you want to learn ASP.Net and perfect yourself in .NET training, our CRB Tech Solutions would be of great support for you. Join us with our updated program in ASP.Net course.

Stay connected to CRB Tech reviews for more technical optimization and other resources.