Authorization in .net Core
Tags: dotnetcore, authorization, claimbasedauthorizatio, dotnet
Published: 2023-03-18 05:23:05

In .NET Core, there are several ways to implement authorization for a web application. Here are some of the most common options:

**Role-based Authorization:** This approach is based on assigning roles to users and restricting access to resources based on those roles. In .NET Core, you can use the `[Authorize(Roles = "Admin")]` attribute to restrict access to specific roles.

**Policy-based Authorization:** This approach is based on defining policies that define who can access a particular resource. In .NET Core, you can use the `[Authorize(Policy = "PolicyName")]` attribute to restrict access based on a policy.

**Claims-based Authorization:** This approach is based on defining claims that represent specific user characteristics or attributes. In .NET Core, you can use the `[Authorize(Policy = "ClaimType:ClaimValue")]` attribute to restrict access based on a claim.

**Custom Authorization:** This approach is based on writing your own authorization logic to determine who can access a particular resource. In .NET Core, you can implement the `IAuthorizationHandler` interface and define your own authorization logic.

In addition to these approaches, .NET Core also provides built-in support for external authentication providers such as Microsoft, Google, and Facebook, as well as support for token-based authentication and authorization using JSON Web Tokens (JWTs).

Overall, .NET Core provides a flexible and powerful authorization framework that can be used to implement a wide range of authorization scenarios in web applications.


##Role-based Authorization 
is an approach to authorization in which access to resources is restricted based on the role(s) assigned to a user. In this approach, users are assigned roles, such as "Admin", "Manager", or "Employee", and access to resources is restricted based on these roles. Here's an example of how to implement role-based authorization in .NET Core using C# code:

**1. Define Roles:** First, define the roles that will be used for authorization. This can be done using the `IdentityRole` class, which is provided by the Microsoft.AspNetCore.Identity package. For example:

```csharp
public static class RoleConstants
{
    public const string Admin = "Admin";
    public const string Manager = "Manager";
    public const string Employee = "Employee";
}

```

**2. Add Roles to Users:** Next, add roles to users based on their roles in the organization. This can be done using the `UserManager` class, which is provided by the `Microsoft.AspNetCore.Identity` package. For example:

```csharp 
var userManager = serviceProvider.GetRequiredService<UserManager<IdentityUser>>();

var user = await userManager.FindByNameAsync("john.doe@example.com");

if (user != null)
{
    await userManager.AddToRoleAsync(user, RoleConstants.Employee);
}

```

**3. Restrict Access to Resources:** Finally, restrict access to resources based on the roles assigned to the user. This can be done using the `[Authorize(Roles = "RoleName")]` attribute, which is provided by the `Microsoft.AspNetCore.Authorization` package. For example:

```csharp
[Authorize(Roles = RoleConstants.Admin)]
public class AdminController : Controller
{
    // Controller code here
}
```

In this example, the `AdminController` class is restricted to users with the "Admin" role. If a user without this role tries to access the controller, they will be denied access.

Overall, Role-based Authorization provides a simple and effective way to restrict access to resources based on the roles assigned to users. With the built-in support provided by .NET Core, it's easy to implement role-based authorization in a web application.

##Policy-based Authorization 
is an approach to authorization in which access to resources is restricted based on policies that define who can access a particular resource. In this approach, policies are defined that specify the conditions under which access to a resource is granted or denied. Here's an example of how to implement policy-based authorization in .NET Core using C# code:

**1. Define Policies:** First, define the policies that will be used for authorization. This can be done using the `AuthorizationPolicy` class, which is provided by the `Microsoft.AspNetCore.Authorization` package. For example:

```csharp
public static class PolicyConstants
{
    public const string RequireAdminRole = "RequireAdminRole";
}

public static class PolicyFactory
{
    public static AuthorizationPolicy RequireAdminRole()
    {
        return new AuthorizationPolicyBuilder()
            .RequireRole(RoleConstants.Admin)
            .Build();
    }
}

```

In this example, the `RequireAdminRole` policy requires the "Admin" role to access a particular resource.

**2. Register Policies:** Next, register the policies with the authorization middleware. This can be done using the `services.AddAuthorization()` method in the `ConfigureServices()` method of the `Startup` class. For example:

```csharp
services.AddAuthorization(options =>
{
    options.AddPolicy(PolicyConstants.RequireAdminRole, PolicyFactory.RequireAdminRole());
});

```
In this example, the `RequireAdminRole` policy is registered with the authorization middleware.

**3. Restrict Access to Resources:** Finally, restrict access to resources based on the policies assigned to the resource. This can be done using the `[Authorize(Policy = "PolicyName")]` attribute, which is provided by the `Microsoft.AspNetCore.Authorization` package. For example:

```csharp 
[Authorize(Policy = PolicyConstants.RequireAdminRole)]
public class AdminController : Controller
{
    // Controller code here
}

```
In this example, the `AdminController` class is restricted to users who meet the policy requirements of the `RequireAdminRole` policy. If a user who does not meet these requirements tries to access the controller, they will be denied access.

Overall, Policy-based Authorization provides a flexible and powerful way to restrict access to resources based on policies that define who can access a particular resource. With the built-in support provided by .NET Core, it's easy to implement policy-based authorization in a web application.


##Claims-based Authorization 
is an approach to authorization in which access to resources is restricted based on the claims associated with a user. In this approach, users are assigned claims, which are pieces of information that describe the user, and access to resources is restricted based on these claims. Here's an example of how to implement claims-based authorization in .NET Core using C# code:

**1. Define Claims:** First, define the claims that will be used for authorization. This can be done using the `ClaimTypes` class, which is provided by the `System.Security.Claims` namespace. For example:

```csharp
public static class ClaimConstants
{
    public const string Role = ClaimTypes.Role;
}

```

In this example, the Role claim is defined as a constant.

**2. Add Claims to Users:** Next, add claims to users based on their attributes. This can be done using the `ClaimsPrincipal` class, which is provided by the `System.Security.Claims` namespace. For example:

```csharp

var identity = new ClaimsIdentity(new[]
{
    new Claim(ClaimConstants.Role, RoleConstants.Admin),
    new Claim(ClaimConstants.Role, RoleConstants.Employee),
}, "AuthenticationType");

var principal = new ClaimsPrincipal(identity);

```

In this example, a ClaimsIdentity is created with two claims, "Admin" and "Employee", and added to a ClaimsPrincipal.

**3. Restrict Access to Resources:** Finally, restrict access to resources based on the claims assigned to the user. This can be done using the [Authorize(ClaimType = "ClaimType", Value = "ClaimValue")] attribute, which is provided by the Microsoft.AspNetCore.Authorization package. For example:

```csharp 
[Authorize(ClaimType = ClaimConstants.Role, Value = RoleConstants.Admin)]
public class AdminController : Controller
{
    // Controller code here
}

```
In this example, the AdminController class is restricted to users with the "Admin" claim. If a user without this claim tries to access the controller, they will be denied access.

Overall, Claims-based Authorization provides a flexible and granular way to restrict access to resources based on the claims associated with a user. With the built-in support provided by .NET Core, it's easy to implement claims-based authorization in a web application.


##Custom Authorization 
in .NET Core allows developers to create their own authorization policies and apply them to controllers or actions. Here's an example of how to implement custom authorization in .NET Core using C# code:

**1. Create a Custom Authorization Handler:** First, create a custom authorization handler that inherits from the `AuthorizationHandler<TRequirement>` class. This class is provided by the Microsoft.AspNetCore.Authorization namespace. For example:

```csharp
public class CustomAuthorizationHandler : AuthorizationHandler<MyRequirement>
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, MyRequirement requirement)
    {
        // Authorization logic here
    }
}

```

In this example, a custom authorization handler named CustomAuthorizationHandler is created to handle a requirement called MyRequirement.

**2. Create a Custom Authorization Requirement:** Next, create a custom authorization requirement that inherits from the IAuthorizationRequirement interface. This interface is provided by the Microsoft.AspNetCore.Authorization namespace. For example:

```csharp 
public class MyRequirement : IAuthorizationRequirement
{
    // Requirement properties here
}
```

In this example, a custom authorization requirement named MyRequirement is created.

**3. Register the Custom Authorization Handler:** Once the custom authorization handler and requirement are defined, register the handler with the dependency injection container in the ConfigureServices method of the Startup class. For example:

```csharp

services.AddSingleton<IAuthorizationHandler, CustomAuthorizationHandler>();

```

In this example, the CustomAuthorizationHandler is registered as a singleton service.

**4. Apply the Authorization Policy:** Finally, apply the custom authorization policy to a controller or action using the [Authorize(Policy = "MyPolicy")] attribute. For example:

```csharp
[Authorize(Policy = "MyPolicy")]
public class MyController : Controller
{
    // Controller code here
}
```

In this example, the MyController class is restricted to users who meet the custom authorization policy defined in MyPolicy.

**5. Define the Authorization Policy:** To define the authorization policy, use the AuthorizationPolicyBuilder class provided by the Microsoft.AspNetCore.Authorization namespace. For example:

```csharp 
var myPolicy = new AuthorizationPolicyBuilder()
    .AddRequirements(new MyRequirement())
    .Build();

services.AddAuthorization(options =>
{
    options.AddPolicy("MyPolicy", myPolicy);
});

```
In this example, an authorization policy named `MyPolicy` is defined using the `AuthorizationPolicyBuilder`. The policy requires the `MyRequirement` to be met for access to the restricted resource.

Overall, Custom Authorization in .NET Core provides a powerful and flexible way to control access to resources in a web application. By defining custom authorization handlers and requirements, developers can implement complex authorization policies tailored to the specific needs of their application.