Implementing Authentication in Dot NET Core Applications Using OAuth 2.0

Introduction

In our current digital world, sharing and accessing sensitive data online happens all the time. Because of this, authentication has become a key part of any web application today. It helps ensure that only the right people can get to specific resources and protects against those who shouldn’t have access. With online threats on the rise, making sure that applications and data are secure is more important than ever. 

One popular way to handle authentication is through OAuth 2.0. This method is built to offer secure authorization without needing to share user passwords. With OAuth 2.0, third-party apps can access user information and take actions on their behalf without ever seeing their usernames or passwords. This makes it a great choice for keeping web, mobile, and desktop applications safe. 

In this blog post, we will look at how to set up OAuth 2.0 authentication in .NET Core applications . By using OAuth 2.0, developers can build applications that are both secure and scalable, allowing trusted identity providers like Google, Facebook, or Microsoft to handle the authentication. OAuth 2.0 offers various ways to authorize access, making it flexible enough to fit different types of applications, from web apps to mobile applications and APIs. 

Before diving into the setup, it’s good to have a basic grasp of what OAuth 2.0 is and how it functions. In the coming sections, we’ll guide you through the steps to set up OAuth 2.0 in .NET Core and show you how to do it in a way that boosts your application’s security. 

What is OAuth 2.0?  

OAuth 2.0 is effective; it is usage of one of the most prominent and simple standards which gives right to third party to use the user’s resources without needing to have to log in because of sharing giving up their login information. It was born in 2012 as an improvement of OAuth 1.0, with the purpose of providing a more secure and flexible method for exercising authorization in the present web, mobile and desktop applications. 

With this system, the applications can be provided with some bit access to data stored on a server while the user does not have to divulge his password. Rather than requiring usernames and passwords, this framework provides authorization tokens (access tokens), which enable the application to perform tasks, such as obtaining particular data. As these tokens are time sensitive, the risk of token theft is reduced substantially. 

An important aspect of OAuth 2.0 is its capability to utilize several different authorization grants such as simplest of which include the use of authorization code, implicit, client credentials, and password grants. This means that it is fit for economies with various application configurations such as web, mobile applications, API and server-server communicate applications. OAuth 2.0 has rapidly become the preferred solution for user authentication and authorization. This is due to the simplicity of its use, its potential for growth, and his connectivity with identity providers such as Google, Facebook, and Microsoft. It is mostly implemented to secure gateways for APIs and which enables developer 

Principles of OAuth2.0 

OAuth 2.0 is one of the most distinctive frameworks in the sense that it has a unique way of managing user resources rather than just verification of a user’s identity. Its goal is to allow different resources such as user information or application program interfaces, to be shared without revealing secured information like passwords. In the same vein, OAuth 2.0 allows a user to permit a third-party application to perform certain functions on their behalf. When the user consents, they get an Access Token. 

Access Token is basically a string that is encrypted and represents the permission of the user, and the scope of the permissions granted. Although OAuth 2.0 doesn’t enforce an exact structure of these tokens, many people use the JSON Web Token (JWT) format. JWTs are helpful because they can include more information such as who the user is, and what he is permitted to do, and much more all in one token. This makes it easier and more efficient to determine whether a person is authorized without having to make a call to the server for verification each time. 

And if we turn to security issues there is another commonplace solution: Access Tokens are often configured to expire with time based on usage. This, of course, prevents someone who has stolen a token from using it forever. On the contrary, OAuth 2.0 is adaptive how it handles token lifetime and its refreshing as well as other related requirements. 

Key Features 

Delegated Access: OAuth 2.0 makes it easier for users because they won’t need to share their log-in details if they want to use an app, so this is safe for them as well and on the other hand, it also keeps the range of action of the third-party apps minimal.  

Token-Based Authentication: OAuth 2.0 never depends on only passwords it goes way further, it requires using secure tokens for identity verification of a user and it means that all the tokens will still require authorization for use which makes it a better way of not providing open access to resources. 

Standardized Protocol: Backing of OAuth 2.0 is the case – as it is in the Standard that has been set by the big providers like Google, Facebook or Microsoft. It makes life easier for developers because they do not need to re-invent the wheel, they can design their systems around standard ones so that they would operate properly with other systems.  

Expiration and Revocation: In issuing of OAuth 2.0 tokens users are given time limits to the tokens in a bid to reduce abuse, apart from this the users or the system can also revoke the tokens at any point in time which in turn reduces the chances of unauthorized use and therefore enhances safety. 

Understanding  How  OAuth2.0  Functions 

OAuth 2.0 agreements exist to allow third party applications (Clients) to access secured data on behalf of users (Resource Owner) without needing to share their password. The process to obtain these tokens begins when the Client is assigned some credentials by the Authorization Server. These credentials consist of a Client ID and a Client Secret, which identify and authenticate the Client during the attempt to request for the token. 

Below is a step-by-step process of how it operates:

Phase 1 Invitation:

A mobile application or a web app, such as a client, is the one that starts the process by sending a request to the Authorization Server. This request contains the Clients ID, the redirect URI (the address where the server is supposed to respond), the requested scope (the level of access being requested) and sometimes the Client Secret depending on the grant type used. So, in a way, the redirection URI allows the Authorization Server to know where to route the token or code once the required conditions are satisfied. 

Server Validation:

The Client’s provided credentials are evaluated by the Authorization Server to check whether the requested scopes are permissible to the Client. Scopes refer to the requests and actions for which the Client would like to make a request, for instance, to request to view some user profile details or to post some content on their behalf.

User Consent:

The Resource Owner, usually the user, interacts with the Authorization Server to either allow or deny the requested access. If the user agrees, they grant their permission, which lets the Client act for them within the agreed-upon scopes.

Response to Client:

Once the user gives their consent, the Authorization Server sends back either an Authorization Code (for authorization code grants) or an Access Token (for implicit or client credentials grants). Sometimes, a Refresh Token is included too, which the Client can use to get a new Access Token when the old one runs out.

Access Resource Server:

With the Access Token in hand, the Client can make secure requests to the Resource Server to retrieve the protected information. The Resource Server checks the token and then provides the requested data or performs the action.

This clear process ensures that access is safe and managed while keeping user privacy and system integrity intact. 

Grant Types in OAuth 2.0

In OAuth 2.0, grants represent the steps a client must take to gain access to a resource. The authorization framework offers different types of grants to handle various situations:

Authorization Code Grant:  Here, the authorization server gives the client a one-time Authorization Code, which is then swapped for an Access Token. This method works best for traditional web apps since the exchange can be safely done on the server.  Single Page Apps(SPAs) and mobile/native apps can also use this flow, but they can’t securely store the client secret. Therefore, the authentication during the exchange relies only on the client ID. A more secure option is the Authorization Code with PKCE.

Implicit Grant: This is a simpler flow where the Access Token goes directly to the client. The authorization server can either return the token as part of the callback URI or as a response from a form. The first method is now less recommended due to risks of token exposure.

Authorization Code Grant with PKCE: Similar to the Authorization Code grant, this flow includes more steps that increase security, making it suitable for mobile/native apps and SPAs.

Resource Owner Credentials Grant Type: In this case, the client needs to get the resource owner’s credentials first, which are sent to the authorization server. This type should only be used by fully trusted clients. It’s beneficial since it doesn’t require redirecting to the authorization server, which is useful when redirection isn’t possible.

Client Credentials Grant Type: This is used for applications that don’t involve user interaction, like automated processes or microservices. Here, the application is authenticated using its client ID and secret.

Device Authorization Flow: This grant helps apps on devices with limited input options, like smart TVs.

Refresh Token Grant: This process involves exchanging a Refresh Token for a new Access Token.