C# Create JWT with Custom Headers and Sign with Private Key

January 7, 2022

I am trying to figure out how to create a JWT in C# that has custom headers and is signed with a private key. My current attempt is as follows and seems to work except I haven’t found a way to include custom headers in it as well.

            string publicKey = File.ReadAllText(@"C:\Users\blah\Desktop\Keys\testpublickey.pem");
            string privateKey = File.ReadAllText(@"C:\Users\blah\Desktop\Keys\testprivatekey.pem");
            var random = new Random();
            int num = random.Next(1000000, 500000000);
            var exp = DateTime.Now.AddMinutes(10).Ticks;

            var claims = new List<Claim>();
            claims.Add(new Claim("iss", "919d1ebb-bf3d-4c03-8855-b72b376db9ad"));
            claims.Add(new Claim("sub", "919d1ebb-bf3d-4c03-8855-b72b376db9ad"));
            claims.Add(new Claim("aud", @"https://api.alt.www.blah.com/auth/oauth/v2/token"));
            claims.Add(new Claim("exp", exp.ToString()));
            claims.Add(new Claim("jti", num.ToString()));
            
            var token = CreateToken(claims, privateKey);

and CreateToken:

    private static string CreateToken(List<Claim> claims, string privateRsaKey)
    {
        RSAParameters rsaParams;
        using (var tr = new StringReader(privateRsaKey))
        {
            var pemReader = new PemReader(tr);

            var privateRsaParams = pemReader.ReadObject() as Org.BouncyCastle.Crypto.Parameters.RsaPrivateCrtKeyParameters;
            rsaParams = DotNetUtilities.ToRSAParameters(privateRsaParams);
        }
        using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
        {
            rsa.ImportParameters(rsaParams);
            Dictionary<string, object> payload = claims.ToDictionary(k => k.Type, v => (object)v.Value);
            return Jose.JWT.Encode(payload, rsa, Jose.JwsAlgorithm.RS256);
        }
    }

How can I add custom headers to a JWT signed with a private key?

>Solution :

Looks like you can pass extra headers to the method Jose.JWT.Encode as an optional parameter: parameter of type IDictionary<string, object> named: extraHeaders

var extraHeaders = new Dictionary<string, object> 
{ 
    ////Your custom headers 
};
 string result = Jose.JWT.Encode(
    payload, rsa, Jose.JwsAlgorithm.RS256, extraHeaders: extraHeaders);

Reference: jose-jwt/JWT.cs