GenerateToken.cs

public static string GenerateToken(string id, int days, string secret)
{
    var tokenDescriptor = new SecurityTokenDescriptor
    {
        Subject = new ClaimsIdentity(new[]
        {
            new Claim(ClaimTypes.Name, id)
        }),
        Expires = DateTime.UtcNow.AddDays(Convert.ToInt32(days)),
        SigningCredentials = new SigningCredentials(
          new SymmetricSecurityKey(Convert.FromBase64String(secret)), 
          SecurityAlgorithms.HmacSha256Signature
        )
    };
    return new JwtSecurityTokenHandler().WriteToken(
      tokenHandler.CreateToken(tokenDescriptor)
    );
}