Jwt Builder and HMACSHA256Algorithm not working

It seems like you're trying to use JWT (JSON Web Token) in a .NET Core 2.1 project, and you're facing issues with the JwtBuilder and HMACSHA256Algorithm. The error you're encountering could be due to the absence of required packages or changes in the library structure.

In more recent versions of .NET Core, the JWT library has undergone some changes, and you may need to use a different library. Here's an example using the System.IdentityModel.Tokens.Jwt namespace, which is commonly used for JWT in .NET Core:

Firstly, you need to install the necessary NuGet package. Open your Package Manager Console and run:

Install-Package System.IdentityModel.Tokens.Jwt -Version 6.15.0

Now, you can create a JWT token using the following code:

using System;
using System.Collections.Generic;
using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using Microsoft.IdentityModel.Tokens;

class Program
{
    static void Main()
    {
        string apiKey = "32a4ef";
        string secretKey = "qloDZF";
        int currtime = 163068;

        var claims = new List
        {
            new Claim("iss", apiKey),
            new Claim("iat", currtime.ToString()),
            new Claim("jti", Guid.NewGuid().ToString())
        };

        var key = new SymmetricSecurityKey(System.Text.Encoding.UTF8.GetBytes(secretKey));
        var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

        var token = new JwtSecurityToken(
            claims: claims,
            expires: DateTime.Now.AddMinutes(30), // Set expiration as needed
            signingCredentials: creds
        );

        var tokenHandler = new JwtSecurityTokenHandler();
        var tokenString = tokenHandler.WriteToken(token);

        Console.WriteLine(tokenString);
    }
}

In this example, we use System.IdentityModel.Tokens.Jwt to create the JWT token. Ensure that you have the correct version of the library installed. If you encounter issues with missing packages, check the version compatibility.

Note: Always use the latest library versions when possible, as there might be security updates and improvements in newer releases.