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ASP.NET Core Web API v2.0: Authorization

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ASP.NET Core Web API v2.0: Authorization

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By Damien Guard

This tutorial demonstrates how to add authorization to an ASP.NET Core Web API using the standard JWT middleware. We recommend you to Log in to follow this quickstart with examples configured for your account.

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System requirements: .NET Core SDK 2.1.300 | .NET Core 2.1.0 | ASP.NET Core 2.1.0 | Visual Studio 2017 15.7 or Visual Studio Code (Optional)

New to Auth0? Learn how Auth0 works and read about implementing API authentication and authorization using the OAuth 2.0 framework.

What is cross-origin authentication?

Configure Auth0 APIs

Limitations

Create an API

In the APIs section of the Auth0 dashboard, click Create API. Provide a name and an identifier for your API, for example https://quickstarts/api. You will use the identifier as an audience later, when you are configuring the Access Token verification. Leave the Signing Algorithm as RS256.

Create API

By default, your API uses RS256 as the algorithm for signing tokens. Since RS256 uses a private/public keypair, it verifies the tokens against the public key for your Auth0 account. The public key is in the JSON Web Key Set (JWKS) format, and can be accessed here.

We recommend using the default RS256 signing algorithm for your API. If you need to use the HS256 algorithm, see the HS256 integration sample.

Configure your application for cross-origin authentication

Define Permissions

Permissions let you define how resources can be accessed on behalf of the user with a given access token. For example, you might choose to grant read access to the messages resource if users have the manager access level, and a write access to that resource if they have the administrator access level.

You can define allowed permissions in the Permissions tab of the Auth0 Dashboard's APIs section.

Configure Permissions

This example uses the read:messages scope.

This example demonstrates:

  • How to check for a JSON Web Token (JWT) in the Authorization header of an incoming HTTP request.

  • How to check if the token is valid, using the JSON Web Key Set (JWKS) for your Auth0 account. To learn more about validating Access Tokens, read the Validate an Access Token tutorial.

Create a cross-origin verification page

Configure the Sample project

The sample code has an appsettings.json file which configures it to use the correct Auth0 Domain and API Identifier for your API. If you download the code from this page while logged in, it will be automatically filled. If you use the example from Github, you will need to fill it yourself.

Error Codes and Descriptions

Validate Access Tokens

Browser testing support

Install dependencies

The seed project references the new ASP.NET Core metapackage (Microsoft.AspNetCore.All), which includes all the NuGet packages that are a part of the ASP.NET Core 2.0 framework.

If you are not using the Microsoft.AspNetCore.All metapackage, add the Microsoft.AspNetCore.Authentication.JwtBearer package to your application.

Configure the middleware

The ASP.NET Core JWT Bearer authentication handler downloads the JSON Web Key Set (JWKS) file with the public key. The handler uses the JWKS file and the public key to verify the Access Token's signature.

In your application, register the authentication services:

  1. Make a call to the AddAuthentication method. Configure the JWT Bearer tokens as the default authentication and challenge schemes.
  2. Make a call to the AddJwtBearer method to register the JWT Bearer authentication scheme. Configure your Auth0 domain as the authority, and your Auth0 API identifier as the audience.

To add the authentication middleware to the middleware pipeline, add a call to the UseAuthentication method:

Validate scopes

To make sure that an Access Token contains the correct scope, use the Policy-Based Authorization in ASP.NET Core.

Create a new authorization requirement called HasScopeRequirement. This requirement checks if the scope claim issued by your Auth0 tenant is present. If the scope claim exists, the requirement checks if the scope claim contains the requested scope.

In your ConfigureServices method, add a call to the AddAuthorization method. To add policies for the scopes, call AddPolicy for each scope. Also ensure that you register the HasScopeHandler as a singleton:

Protect API Endpoints

The JWT middleware integrates with the standard ASP.NET Core Authentication and Authorization mechanisms.

To secure an endpoint, you need to add the [Authorize] attribute to your controller action:

To secure endpoints that require specific scopes, we need to make sure that the correct scope is present in the access_token. To do that, add the Authorize attribute to the Scoped action, passing read:messages as the policy parameter.

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