Generate JSON Web Key (jwk) in c#

user_649384 0
Viewed 3194

I need to generate JSON Web Key (jwk) using c# as shown. I have gone through a few articles but there were implementations in other languages such as Java and there was a third-party library (Nimbus JOSE+JWT library and so). Could you please help me to generate JSON Web Key in C#?

{
    "e": "AQAB",
    "n": "nZD7QWmIwj-3N_RZ1qJjX6CdibU87y2l02yMay4KunambalP9g0fU9yZLwLX9WYJINcXZDUf6QeZ-SSbblET-h8Q4OvfSQ7iuu0WqcvBGy8M0qoZ7I-NiChw8dyybMJHgpiP_AyxpCQnp3bQ6829kb3fopbb4cAkOilwVRBYPhRLboXma0cwcllJHPLvMp1oGa7Ad8osmmJhXhM9qdFFASg_OCQdPnYVzp8gOFeOGwlXfSFEgt5vgeU25E-ycUOREcnP7BnMUk7wpwYqlE537LWGOV5z_1Dqcqc9LmN-z4HmNV7b23QZW4_mzKIOY4IqjmnUGgLU9ycFj5YGDCts7Q",
    "alg": "RS256",
    "kid": "8f796169-0ac4-48a3-a202-fa4f3d814fcd",
    "kty": "RSA",
    "use": "sig"
}
jwk jwt c#
2 Answers

Christos's comment above points in the correct direction, however the class you actually want is JsonWebKeyConverter. in the Microsoft.IdentityModel.Tokens nuget package.

Assuming you have your public key file available somewhere then you would want the following code:

var cert = new X509Certificate2(@".\CertPublicKey.cer");
var key = new X509SecurityKey(cert);
var jwk = JsonWebKeyConverter.ConvertFromX509SecurityKey(key, true);
user_4234600

No need to run this through a X509 cert. You can easily serialize the JSON to a Microsoft.IdentityModel.Tokens.JsonWebKey object using the .Create(string json) constructor.

You can either pass in your JSON (after removing line breaks and escaping quotes),

string str_jwk = "{\"e\":\"AQAB\",\"n\":\"nZD7QWmIwj-3N_RZ1qJjX6CdibU87y2l02yMay4KunambalP9g0fU9yZLwLX9WYJINcXZDUf6QeZ-SSbblET-h8Q4OvfSQ7iuu0WqcvBGy8M0qoZ7I-NiChw8dyybMJHgpiP_AyxpCQnp3bQ6829kb3fopbb4cAkOilwVRBYPhRLboXma0cwcllJHPLvMp1oGa7Ad8osmmJhXhM9qdFFASg_OCQdPnYVzp8gOFeOGwlXfSFEgt5vgeU25E-ycUOREcnP7BnMUk7wpwYqlE537LWGOV5z_1Dqcqc9LmN-z4HmNV7b23QZW4_mzKIOY4IqjmnUGgLU9ycFj5YGDCts7Q\",\"alg\":\"RS256\",\"kid\":\"8f796169-0ac4-48a3-a202-fa4f3d814fcd\",\"kty\":\"RSA\",\"use\":\"sig\"}";

Or use Notepad++ to Base64 encode (Plugins -> MIME Tools -> Base64 Encode with padding), then decode with:

string encoded_value = "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";
string str_jwk = Encoding.UTF8.GetString(Convert.FromBase64String(encoded_value))

Then:

var jwk = JsonWebKey.Create(str_jwk);

That will give you your JWK. My question to you is, how do you then use it to sign a JWT? That's what I'm pulling my hair out over. (Under .NET Framework 4.8. I know there are some much better helper classes available in .NET 5/6.)

user_18435500
Related