JWT Signing using RSASSA-PSS in .NET Core

29 July 2019 C#

As of version 5.5, Microsoft’s IdentityModel library now supports the signing of JSON Web Tokens using the RSASSA-PSS (Probabilistic Signature Scheme) digital signature algorithm. This is great news if you’re looking to start building .NET Core systems that implement OpenID’s Financial-grade API and Open Banking, where PS256 should be used for signing.

You can find the full list of support for various .NET targets on GitHub, but the exciting thing is that PS256, PS384, and PS512 are now supported on .NET Core.

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JSON Web Encryption (JWE) in .NET Core

14 January 2019 C#

A signed JSON Web Token (JWT) is one of the most useful and common constructs you’ll see floating around modern security systems. These tokens give us a simple, secure structure in which to transfer data and verify that it has not been tampered with. However, what about when we need to send sensitive data within a JWT?

To solve this issue, we have JSON Web Encryption (JWE), enabling us to encrypt a token so that only the intended recipient can read it.

In this article, we’re going to look at how we can protect sensitive data within our JWTs in .NET Core, using JWEs and the various token libraries available to us.

.NET Core

JWE Format

We’re going to use JWE Compact Serialization (as opposed to JWE JSON Serialization), which looks something like the following...

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JWT Signing using ECDSA in .NET Core

02 February 2018 C#

Recently, as part of messing around with an identity provider, I was given the following private/public key pair and told to sign a JSON Web Token (JWT) with them using ES256:

Private: c711e5080f2b58260fe19741a7913e8301c1128ec8e80b8009406e5047e6e1ef
Public: 04e33993f0210a4973a94c26667007d1b56fe886e8b3c2afdd66aa9e4937478ad20acfbdc666e3cec3510ce85d40365fc2045e5adb7e675198cf57c6638efa1bdb

Okay, sounds simple enough. 5 days and a lot of swearing later, I finally got it working. Now I’m going to write it down so that I don’t have to go through it again.

.NET Core

In .NET Core, to sign a JWT using an Elliptic Curve Digital Signature Algorithm (ECDSA) we need to get ourselves an instance of ECDsaSecurityKey. The constructor for this takes in an instance of ECDsa, which in turn we have to pass in an instance of ECParameters if we want to load in our own key and not have it generate one for us. So, let’s make a start!

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Deserializing a JSON Enumerated String to a Different C# Enumerated Type

22 June 2015 C#

Problem

Recently I had to use a Webhook that returned an enumerated string that was very different from the enum it was supposed to convert to (in this case the JSON used snake case, C# used camel case).

Oddly enough, I knew the solution for this when receiving XML but I was a bit stumped when it came to dealing with JSON.

I could have received the JSON string and then manually mapped out the entire enum within my business logic, but I wanted to handle this during deserialization with decent performance whilst still mapping the enum and its associated string in one easily maintainable location.

Solution

The solution was to use some of the methods and attributes in Newtonsoft.JSON, you know, that package that everything else is dependent on but you never seem to use. This makes use of...

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