feat: implement token generation and issuing on successful login

src/FiscalOS.API/Login/TokenService.cs

@@ -0,0 +1,67 @@
+using System.IdentityModel.Tokens.Jwt;
+using System.Security.Claims;
+using System.Security.Cryptography;
+using System.Text;
+
+using FiscalOS.Core.Identity;
+
+using Microsoft.Extensions.Options;
+using Microsoft.IdentityModel.Tokens;
+
+namespace FiscalOS.API.Login;
+
+internal sealed class TokenService(
+  TimeProvider timeProvider,
+  IOptions<JwtOptions> jwtOptions
+)
+{
+  private const int RefreshTokenExpiryInHours = 12;
+  private readonly JwtOptions _jwtOptions = jwtOptions.Value;
+  private readonly TimeProvider _timeProvider = timeProvider;
+
+  public string GenerateAccessToken(User user)
+  {
+    var tokenHandler = new JwtSecurityTokenHandler();
+    var secretKeyBytes = Encoding.UTF8.GetBytes(_jwtOptions.Secret);
+    var issuedAt = _timeProvider.GetUtcNow();
+    var expiresAt = issuedAt.AddMinutes(_jwtOptions.ExpiryInMinutes);
+    List<Claim> claims = [
+      new(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
+      new(JwtRegisteredClaimNames.Sub, user.Id.ToString()),
+    ];
+
+    var descriptor = new SecurityTokenDescriptor()
+    {
+      Subject = new(claims),
+      IssuedAt = issuedAt.UtcDateTime,
+      Expires = expiresAt.UtcDateTime,
+      Issuer = _jwtOptions.Issuer,
+      Audience = _jwtOptions.Audience,
+      SigningCredentials = new(
+        new SymmetricSecurityKey(secretKeyBytes),
+        SecurityAlgorithms.HmacSha256Signature
+      ),
+    };
+
+    var securityToken = tokenHandler.CreateJwtSecurityToken(descriptor);
+    var jwtToken = tokenHandler.WriteToken(securityToken);
+
+    return jwtToken;
+  }
+
+  public RefreshToken GenerateRefreshToken(User user)
+  {
+    var expiresAt = _timeProvider
+      .GetUtcNow()
+      .AddHours(RefreshTokenExpiryInHours);
+
+    return RefreshToken.From(user.Id, GenerateToken(), expiresAt);
+  }
+
+  private static string GenerateToken()
+  {
+    var randomBytes = RandomNumberGenerator.GetBytes(32);
+    var token = Convert.ToBase64String(randomBytes);
+    return token;
+  }
+}