FlowAPI.Application/Services/TokenService.cs

using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;
using FlowAPI.Application.Interfaces;
using FlowAPI.Domain.Entities;
using Microsoft.Extensions.Configuration;
using Microsoft.IdentityModel.Tokens;

namespace FlowAPI.Application.Services
{
    public class TokenService : ITokenService
    {
        private readonly SymmetricSecurityKey _key;
        private readonly IConfiguration _config;

        public TokenService(IConfiguration config)
        {
            _config = config;
            var secretKey = _config["Jwt:Key"] ?? throw new ArgumentNullException("Jwt:Key is missing in configuration.");
            _key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(secretKey));
        }

        public string CreateToken(User user)
        {
            var claims = new List<Claim>
            {
                new Claim(JwtRegisteredClaimNames.NameId, user.Id.ToString()),
                new Claim(JwtRegisteredClaimNames.Email, user.Email),
                new Claim("displayName", user.DisplayName)
            };

            var creds = new SigningCredentials(_key, SecurityAlgorithms.HmacSha256Signature);

            var tokenDescriptor = new SecurityTokenDescriptor
            {
                Subject = new ClaimsIdentity(claims),
                Expires = DateTime.Now.AddDays(double.Parse(_config["Jwt:ExpiryDays"] ?? "14")),
                SigningCredentials = creds,
                Issuer = _config["Jwt:Issuer"],
                Audience = _config["Jwt:Audience"]
            };

            var tokenHandler = new JwtSecurityTokenHandler();
            var token = tokenHandler.CreateToken(tokenDescriptor);

            return tokenHandler.WriteToken(token);
        }
    }
}