JWT refresh tokens and .NET Core

In this article, I will present to you a basic implementation of the refresh token mechanism that you can extend to your own needs.


 

Let’s start with the need of using the refresh tokens. When you make use of the token authentication (e.g. OAuth) and pass the tokens via Authorization HTTP header, usually, these tokens have a specific expiration time. Whether it’s a minute, 10 minutes, an hour or a week makes no big difference, as long as you can provide a way to generate the new token.

Most likely, you don’t want the user to login every time that the token expiration hits its limit. On the other hand, you don’t want to store the user credentials (email, login, password etc.) somewhere in memory (whether it’s a device, cookie or a local storage). What can you do then? Store the so-called refresh tokens instead, that can be used to recreate the access tokens.

You can download the whole sample by cloning a repository and the HTTP requests available as the Postman collection. Now, let’s start with the implementation, just beware that I’m not following here any specialized patterns, rich domain models and so on – it’s just a sample that works, not a sophisticated solution.

At first, let’s start with the models that we’re going to use:

These should be rather straightforward. You might also notice, that we will be able to revoke the refresh token, so it can’t be used anymore if the user wishes so.

This is how we could define the business logic:

Into my AccountService implementation, I’ll inject the following services:

The IJwtHandler (which is responsible for generating JSON Web Tokens) can be found in a repository and the IPasswordHasher comes from Microsoft.AspNetCore.Identity namespace.

Let’s focus now on refreshing and revoking the tokens:

The logic is very simple here – just ensure that the refresh token exists and that it was not already revoked, so it can be used again and again. And when to create a new refresh token? For example, when the user authenticates:

It’s up to you how the refresh token is going to look like, I decided to create a unique GUID and then make use of IPasswordHasher to create a secure, random string.

And pretty much that’s it, we can define the following controller in our API to see if everything works as expected:

22 Comments JWT refresh tokens and .NET Core

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  2. Danny

    Thanks for the write-up! Lots of information out there on JWTs, but limited implementations for Refresh Tokens. I found this article incredibly helpful (:

    Reply
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      1. andrei

        Anyway, Piotr, I don’t want be annoying, and appreciate you willigness to share thougths across the internet.
        The question – who is the audience your post ?
        a) the person, who doesn’t familiar deeply with the workflow of OAuth2 and wants quickly integrate this technology into own project? – so no, a lot of meaningful steps are missing.
        b) the person, who familiar with OAuth2 workflow and wants to find some knowledge gaps, f.e. implementation of refresh token flow? – no, this post covers only high level contracts (AccountController, IAccountService) without any IMPORTANT implementation details of JWT token and refresh token(as post titled).

        So, post looks mostly, like a note (some reminder) personally for you, because I have wasted more, than “4 minutes to read” and have tried to find coherence of your pieces of code.

        Reply
        1. Piotr Gankiewicz

          It has nothing to do with the OAuth2, which is huge and complicated.The point was to show what refreshing token is all about, and how easily you can implement it, given that you use JWT which is a good fit for most apps. There’s a link to the repository where you can clone the working code, and if by important details you mean missing implementation of SQL repository (or any other data persistence system), well, that’s not really important.

          Reply

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