Merge branch 'feature/auth-2fa-security' into main

Auth/registration/account-security overhaul: per-account lockout,
TOTP 2FA (RFC 6238) with recovery codes, trusted devices (30-day 2FA
skip), configurable email verification enforcement, and server-tracked
sessions (view/revoke/sign-out-others). Full security-settings UI and
login/OAuth 2FA challenge step.

# Conflicts:
#	JobTrackerApi/Services/StartupInitializationExtensions.cs

JobTrackerApi/Services/AppSessionIssuer.cs

@@ -0,0 +1,41 @@
+using System.Security.Cryptography;
+using JobTrackerApi.Data;
+using JobTrackerApi.Models;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Configuration;
+
+namespace JobTrackerApi.Services;
+
+// Shared by AuthController (local/Google/Microsoft sign-in) and TwoFactorController (the
+// post-challenge sign-in) so the httpOnly session cookie + readable CSRF cookie are always
+// issued the same way, from one place. Also the single place a UserSession row is created, so
+// every JWT this app ever hands out has a matching server-side row Program.cs can revoke.
+public static class AppSessionIssuer
+{
+    public static async Task IssueAsync(HttpRequest request, HttpResponse response, ITokenService tokens, JobTrackerContext db, IConfiguration cfg, ApplicationUser user, bool rememberMe, CancellationToken cancellationToken)
+    {
+        var minutes = cfg.GetValue("Auth:JwtExpiresMinutes", 60 * 12);
+        if (minutes < 5) minutes = 5;
+        if (minutes > 60 * 24 * 30) minutes = 60 * 24 * 30;
+
+        var now = DateTimeOffset.UtcNow;
+        var session = new UserSession
+        {
+            Id = Guid.NewGuid().ToString("N"),
+            UserId = user.Id,
+            DeviceLabel = TrustedDeviceService.DescribeUserAgent(request.Headers["User-Agent"].ToString()),
+            CreatedAtUtc = now,
+            LastSeenAtUtc = now,
+            ExpiresAtUtc = now.AddMinutes(minutes),
+        };
+        db.UserSessions.Add(session);
+        await db.SaveChangesAsync(cancellationToken);
+
+        var token = await tokens.CreateAccessTokenAsync(user, session.Id, cancellationToken);
+        var secure = request.IsHttps || string.Equals(request.Headers["X-Forwarded-Proto"], "https", StringComparison.OrdinalIgnoreCase);
+        response.Cookies.Append(AuthSessionOptions.SessionCookieName, token, AuthSessionOptions.BuildSessionCookie(rememberMe, secure));
+
+        var csrf = Convert.ToHexString(RandomNumberGenerator.GetBytes(32)).ToLowerInvariant();
+        response.Cookies.Append(AuthSessionOptions.CsrfCookieName, csrf, AuthSessionOptions.BuildCsrfCookie(rememberMe, secure));
+    }
+}

JobTrackerApi/Services/AuthSessionOptions.cs

@@ -7,6 +7,7 @@ public static class AuthSessionOptions
     public const string SessionCookieName = "jobtracker_auth";
     public const string CsrfCookieName = "XSRF-TOKEN";
     public const string CsrfHeaderName = "X-CSRF-TOKEN";
+    public const string TrustedDeviceCookieName = "jobtracker_td";
 
     public static CookieOptions BuildSessionCookie(bool persistent, bool secure)
     {
@@ -75,4 +76,35 @@ public static class AuthSessionOptions
             MaxAge = TimeSpan.Zero,
         };
     }
+
+    // Stricter than the session cookie (SameSite=Strict, never HttpOnly=false): this cookie's
+    // only job is "skip the 2FA prompt", so it must never be readable by JS and should not even
+    // be sent on cross-site navigations.
+    public static CookieOptions BuildTrustedDeviceCookie(bool secure)
+    {
+        return new CookieOptions
+        {
+            HttpOnly = true,
+            IsEssential = true,
+            SameSite = SameSiteMode.Strict,
+            Secure = secure,
+            Path = "/",
+            Expires = DateTimeOffset.UtcNow.AddDays(30),
+            MaxAge = TimeSpan.FromDays(30),
+        };
+    }
+
+    public static CookieOptions BuildExpiredTrustedDeviceCookie(bool secure)
+    {
+        return new CookieOptions
+        {
+            HttpOnly = true,
+            IsEssential = true,
+            SameSite = SameSiteMode.Strict,
+            Secure = secure,
+            Path = "/",
+            Expires = DateTimeOffset.UnixEpoch,
+            MaxAge = TimeSpan.Zero,
+        };
+    }
 }

JobTrackerApi/Services/LocalSessionValidator.cs

@@ -0,0 +1,30 @@
+using System.Security.Claims;
+using JobTrackerApi.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace JobTrackerApi.Services;
+
+// The actual revocation check behind Program.cs's "local" JwtBearer OnTokenValidated. Pulled out
+// of Program.cs so it's unit-testable without standing up a full TestServer/HTTP pipeline.
+public static class LocalSessionValidator
+{
+    public static async Task<bool> IsValidAsync(JobTrackerContext db, ClaimsPrincipal? principal, DateTimeOffset now, CancellationToken cancellationToken = default)
+    {
+        var sid = principal?.FindFirst("sid")?.Value;
+        // Fail closed: see the comment on the OnTokenValidated wiring in Program.cs for why a
+        // missing sid is rejected rather than grandfathered in.
+        if (string.IsNullOrWhiteSpace(sid)) return false;
+
+        var session = await db.UserSessions.IgnoreQueryFilters()
+            .FirstOrDefaultAsync(x => x.Id == sid, cancellationToken);
+        if (session is null || session.RevokedAtUtc is not null || session.ExpiresAtUtc <= now) return false;
+
+        if (now - session.LastSeenAtUtc > TimeSpan.FromMinutes(5))
+        {
+            session.LastSeenAtUtc = now;
+            await db.SaveChangesAsync(cancellationToken);
+        }
+
+        return true;
+    }
+}

JobTrackerApi/Services/StartupInitializationExtensions.cs

@@ -244,6 +244,9 @@ public static class StartupInitializationExtensions
             `MicrosoftSubject` longtext NULL,
             `MicrosoftEmail` longtext NULL,
             `MicrosoftLinkedAt` datetime(6) NULL,
+            `TotpSecretEncrypted` longtext NULL,
+            `TotpPendingSecretEncrypted` longtext NULL,
+            `TotpEnabledAtUtc` datetime(6) NULL,
             PRIMARY KEY (`Id`)
         ) CHARACTER SET=utf8mb4;
 
@@ -359,7 +362,10 @@ public static class StartupInitializationExtensions
             "GoogleLinkedAt" TEXT NULL,
             "MicrosoftSubject" TEXT NULL,
             "MicrosoftEmail" TEXT NULL,
-            "MicrosoftLinkedAt" TEXT NULL
+            "MicrosoftLinkedAt" TEXT NULL,
+            "TotpSecretEncrypted" TEXT NULL,
+            "TotpPendingSecretEncrypted" TEXT NULL,
+            "TotpEnabledAtUtc" TEXT NULL
         );
         """);
 
@@ -440,6 +446,9 @@ public static class StartupInitializationExtensions
                 EnsureColumn(conn, "AspNetUsers", "MicrosoftSubject", "ALTER TABLE AspNetUsers ADD COLUMN MicrosoftSubject TEXT NULL;");
                 EnsureColumn(conn, "AspNetUsers", "MicrosoftEmail", "ALTER TABLE AspNetUsers ADD COLUMN MicrosoftEmail TEXT NULL;");
                 EnsureColumn(conn, "AspNetUsers", "MicrosoftLinkedAt", "ALTER TABLE AspNetUsers ADD COLUMN MicrosoftLinkedAt TEXT NULL;");
+                EnsureColumn(conn, "AspNetUsers", "TotpSecretEncrypted", "ALTER TABLE AspNetUsers ADD COLUMN TotpSecretEncrypted TEXT NULL;");
+                EnsureColumn(conn, "AspNetUsers", "TotpPendingSecretEncrypted", "ALTER TABLE AspNetUsers ADD COLUMN TotpPendingSecretEncrypted TEXT NULL;");
+                EnsureColumn(conn, "AspNetUsers", "TotpEnabledAtUtc", "ALTER TABLE AspNetUsers ADD COLUMN TotpEnabledAtUtc TEXT NULL;");
 
                 static void EnsureUserRuleSettingsTable(DbConnection c)
                 {
@@ -623,10 +632,63 @@ public static class StartupInitializationExtensions
                     Exec(c, """CREATE INDEX IF NOT EXISTS "IX_TailoredCvDrafts_JobApplicationId" ON "TailoredCvDrafts" ("JobApplicationId");""");
                 }
 
+                static void EnsureTwoFactorRecoveryCodesTable(DbConnection c)
+                {
+                    Exec(c, """
+        CREATE TABLE IF NOT EXISTS "TwoFactorRecoveryCodes" (
+            "Id" INTEGER NOT NULL CONSTRAINT "PK_TwoFactorRecoveryCodes" PRIMARY KEY AUTOINCREMENT,
+            "UserId" TEXT NOT NULL,
+            "CodeHash" TEXT NOT NULL,
+            "CreatedAtUtc" TEXT NOT NULL,
+            "UsedAtUtc" TEXT NULL
+        );
+        """);
+
+                    Exec(c, """CREATE INDEX IF NOT EXISTS "IX_TwoFactorRecoveryCodes_UserId_UsedAtUtc" ON "TwoFactorRecoveryCodes" ("UserId", "UsedAtUtc");""");
+                }
+
+                static void EnsureTrustedDevicesTable(DbConnection c)
+                {
+                    Exec(c, """
+        CREATE TABLE IF NOT EXISTS "TrustedDevices" (
+            "Id" INTEGER NOT NULL CONSTRAINT "PK_TrustedDevices" PRIMARY KEY AUTOINCREMENT,
+            "UserId" TEXT NOT NULL,
+            "TokenHash" TEXT NOT NULL,
+            "DeviceLabel" TEXT NULL,
+            "CreatedAtUtc" TEXT NOT NULL,
+            "LastSeenAtUtc" TEXT NOT NULL,
+            "ExpiresAtUtc" TEXT NOT NULL
+        );
+        """);
+
+                    Exec(c, """CREATE INDEX IF NOT EXISTS "IX_TrustedDevices_UserId" ON "TrustedDevices" ("UserId");""");
+                    Exec(c, """CREATE INDEX IF NOT EXISTS "IX_TrustedDevices_TokenHash" ON "TrustedDevices" ("TokenHash");""");
+                }
+
+                static void EnsureUserSessionsTable(DbConnection c)
+                {
+                    Exec(c, """
+        CREATE TABLE IF NOT EXISTS "UserSessions" (
+            "Id" TEXT NOT NULL CONSTRAINT "PK_UserSessions" PRIMARY KEY,
+            "UserId" TEXT NOT NULL,
+            "DeviceLabel" TEXT NULL,
+            "CreatedAtUtc" TEXT NOT NULL,
+            "LastSeenAtUtc" TEXT NOT NULL,
+            "ExpiresAtUtc" TEXT NOT NULL,
+            "RevokedAtUtc" TEXT NULL
+        );
+        """);
+
+                    Exec(c, """CREATE INDEX IF NOT EXISTS "IX_UserSessions_UserId" ON "UserSessions" ("UserId");""");
+                }
+
                 EnsureGmailConnectionsTable(conn);
                 EnsureMicrosoftGraphConnectionsTable(conn);
                 EnsureImapConnectionsTable(conn);
                 EnsureCvTables(conn);
+                EnsureTwoFactorRecoveryCodesTable(conn);
+                EnsureTrustedDevicesTable(conn);
+                EnsureUserSessionsTable(conn);
 
                 // Legacy DB signature: migration history exists (AddCorrespondence applied), but 20260310195000 not recorded,
                 // and at least one of the new columns already exists.
@@ -780,6 +842,9 @@ public static class StartupInitializationExtensions
                     EnsureMySqlColumn(conn, "AspNetUsers", "MicrosoftSubject", "ALTER TABLE `AspNetUsers` ADD COLUMN `MicrosoftSubject` longtext NULL;");
                     EnsureMySqlColumn(conn, "AspNetUsers", "MicrosoftEmail", "ALTER TABLE `AspNetUsers` ADD COLUMN `MicrosoftEmail` longtext NULL;");
                     EnsureMySqlColumn(conn, "AspNetUsers", "MicrosoftLinkedAt", "ALTER TABLE `AspNetUsers` ADD COLUMN `MicrosoftLinkedAt` datetime NULL;");
+                    EnsureMySqlColumn(conn, "AspNetUsers", "TotpSecretEncrypted", "ALTER TABLE `AspNetUsers` ADD COLUMN `TotpSecretEncrypted` longtext NULL;");
+                    EnsureMySqlColumn(conn, "AspNetUsers", "TotpPendingSecretEncrypted", "ALTER TABLE `AspNetUsers` ADD COLUMN `TotpPendingSecretEncrypted` longtext NULL;");
+                    EnsureMySqlColumn(conn, "AspNetUsers", "TotpEnabledAtUtc", "ALTER TABLE `AspNetUsers` ADD COLUMN `TotpEnabledAtUtc` datetime NULL;");
 
                     if (!HasMySqlTable(conn, "RuleSettings"))
                     {
@@ -988,6 +1053,84 @@ public static class StartupInitializationExtensions
                         cmd.ExecuteNonQuery();
                     }
 
+                    if (!HasMySqlTable(conn, "TwoFactorRecoveryCodes"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = @"CREATE TABLE IF NOT EXISTS `TwoFactorRecoveryCodes` (
+        `Id` int NOT NULL AUTO_INCREMENT,
+        `UserId` varchar(255) NOT NULL,
+        `CodeHash` varchar(255) NOT NULL,
+        `CreatedAtUtc` datetime(6) NOT NULL,
+        `UsedAtUtc` datetime(6) NULL,
+        PRIMARY KEY (`Id`)
+        );";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    EnsureMySqlAutoIncrementPrimaryKey(conn, "TwoFactorRecoveryCodes", "Id");
+
+                    if (!MySqlIndexExists(conn, "TwoFactorRecoveryCodes", "IX_TwoFactorRecoveryCodes_UserId_UsedAtUtc"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = "CREATE INDEX `IX_TwoFactorRecoveryCodes_UserId_UsedAtUtc` ON `TwoFactorRecoveryCodes` (`UserId`, `UsedAtUtc`);";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    if (!HasMySqlTable(conn, "TrustedDevices"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = @"CREATE TABLE IF NOT EXISTS `TrustedDevices` (
+        `Id` int NOT NULL AUTO_INCREMENT,
+        `UserId` varchar(255) NOT NULL,
+        `TokenHash` varchar(255) NOT NULL,
+        `DeviceLabel` varchar(255) NULL,
+        `CreatedAtUtc` datetime(6) NOT NULL,
+        `LastSeenAtUtc` datetime(6) NOT NULL,
+        `ExpiresAtUtc` datetime(6) NOT NULL,
+        PRIMARY KEY (`Id`)
+        );";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    EnsureMySqlAutoIncrementPrimaryKey(conn, "TrustedDevices", "Id");
+
+                    if (!MySqlIndexExists(conn, "TrustedDevices", "IX_TrustedDevices_UserId"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = "CREATE INDEX `IX_TrustedDevices_UserId` ON `TrustedDevices` (`UserId`);";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    if (!MySqlIndexExists(conn, "TrustedDevices", "IX_TrustedDevices_TokenHash"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = "CREATE INDEX `IX_TrustedDevices_TokenHash` ON `TrustedDevices` (`TokenHash`);";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    if (!HasMySqlTable(conn, "UserSessions"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = @"CREATE TABLE IF NOT EXISTS `UserSessions` (
+        `Id` varchar(64) NOT NULL,
+        `UserId` varchar(255) NOT NULL,
+        `DeviceLabel` varchar(255) NULL,
+        `CreatedAtUtc` datetime(6) NOT NULL,
+        `LastSeenAtUtc` datetime(6) NOT NULL,
+        `ExpiresAtUtc` datetime(6) NOT NULL,
+        `RevokedAtUtc` datetime(6) NULL,
+        PRIMARY KEY (`Id`)
+        );";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    if (!MySqlIndexExists(conn, "UserSessions", "IX_UserSessions_UserId"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = "CREATE INDEX `IX_UserSessions_UserId` ON `UserSessions` (`UserId`);";
+                        cmd.ExecuteNonQuery();
+                    }
+
                     // Schema reconciliation must never crash app startup: an index that fails
                     // (e.g. combined key exceeds MySQL's 3072-byte limit because an older
                     // migration made OwnerUserId wider than the varchar(255) this reconciler

JobTrackerApi/Services/TokenService.cs

@@ -10,7 +10,7 @@ namespace JobTrackerApi.Services;
 
 public interface ITokenService
 {
-    Task<string> CreateAccessTokenAsync(ApplicationUser user, CancellationToken cancellationToken = default);
+    Task<string> CreateAccessTokenAsync(ApplicationUser user, string? sessionId = null, CancellationToken cancellationToken = default);
 }
 
 public sealed class TokenService : ITokenService
@@ -24,7 +24,7 @@ public sealed class TokenService : ITokenService
         _users = users;
     }
 
-    public async Task<string> CreateAccessTokenAsync(ApplicationUser user, CancellationToken cancellationToken = default)
+    public async Task<string> CreateAccessTokenAsync(ApplicationUser user, string? sessionId = null, CancellationToken cancellationToken = default)
     {
         var jwtKey = (_cfg["Auth:JwtKey"] ?? "").Trim();
         if (string.IsNullOrWhiteSpace(jwtKey))
@@ -57,6 +57,9 @@ public sealed class TokenService : ITokenService
         foreach (var r in roles)
             claims.Add(new Claim(ClaimTypes.Role, r));
 
+        if (!string.IsNullOrWhiteSpace(sessionId))
+            claims.Add(new Claim("sid", sessionId));
+
         var now = DateTime.UtcNow;
 
         var token = new JwtSecurityToken(

JobTrackerApi/Services/TrustedDeviceService.cs

@@ -0,0 +1,115 @@
+using System.Security.Cryptography;
+using System.Text;
+using JobTrackerApi.Data;
+using JobTrackerApi.Models;
+using Microsoft.AspNetCore.Http;
+using Microsoft.EntityFrameworkCore;
+
+namespace JobTrackerApi.Services;
+
+// "Trust this device for 30 days" -- lets a 2FA challenge be skipped on the same browser for a
+// month. Shared by AuthController (checks the cookie before gating on 2FA) and
+// TwoFactorController (issues/lists/revokes the cookie's backing row). Never stores the
+// plaintext token, only its SHA-256 hash.
+public static class TrustedDeviceService
+{
+    private static readonly TimeSpan Lifetime = TimeSpan.FromDays(30);
+
+    // Only returns true (and thus skips 2FA) when the cookie's hash matches a non-expired row
+    // for THIS SPECIFIC user -- UserId is part of the DB query itself, not a check applied
+    // after the fact, so a trusted-device cookie minted for user A can never skip 2FA for user
+    // B even if somehow presented on their request.
+    public static async Task<bool> IsDeviceTrustedAsync(JobTrackerContext db, HttpRequest request, string userId, CancellationToken cancellationToken)
+    {
+        var token = request.Cookies[AuthSessionOptions.TrustedDeviceCookieName];
+        if (string.IsNullOrWhiteSpace(token)) return false;
+
+        var hash = HashToken(token);
+        var now = DateTimeOffset.UtcNow;
+        // SQLite/Pomelo cannot translate DateTimeOffset relational comparisons (>) to SQL, so the
+        // expiry check has to happen after materializing the row -- fine here since the equality
+        // filters (UserId, TokenHash) already narrow this to at most one row.
+        var match = await db.TrustedDevices
+            .IgnoreQueryFilters()
+            .FirstOrDefaultAsync(x => x.UserId == userId && x.TokenHash == hash, cancellationToken);
+        if (match is null || match.ExpiresAtUtc <= now) return false;
+
+        match.LastSeenAtUtc = now;
+        await db.SaveChangesAsync(cancellationToken);
+        return true;
+    }
+
+    public static async Task IssueAsync(JobTrackerContext db, HttpRequest request, HttpResponse response, string userId, CancellationToken cancellationToken)
+    {
+        var token = Convert.ToHexString(RandomNumberGenerator.GetBytes(32)).ToLowerInvariant();
+        var now = DateTimeOffset.UtcNow;
+
+        db.TrustedDevices.Add(new TrustedDevice
+        {
+            UserId = userId,
+            TokenHash = HashToken(token),
+            DeviceLabel = DescribeUserAgent(request.Headers["User-Agent"].ToString()),
+            CreatedAtUtc = now,
+            LastSeenAtUtc = now,
+            ExpiresAtUtc = now.Add(Lifetime),
+        });
+        await db.SaveChangesAsync(cancellationToken);
+
+        var secure = request.IsHttps || string.Equals(request.Headers["X-Forwarded-Proto"], "https", StringComparison.OrdinalIgnoreCase);
+        response.Cookies.Append(AuthSessionOptions.TrustedDeviceCookieName, token, AuthSessionOptions.BuildTrustedDeviceCookie(secure));
+    }
+
+    public static void ClearCookie(HttpRequest request, HttpResponse response)
+    {
+        var secure = request.IsHttps || string.Equals(request.Headers["X-Forwarded-Proto"], "https", StringComparison.OrdinalIgnoreCase);
+        response.Cookies.Delete(AuthSessionOptions.TrustedDeviceCookieName, AuthSessionOptions.BuildExpiredTrustedDeviceCookie(secure));
+    }
+
+    // Used to flag "this device" in the trusted-devices list without ever sending a token or
+    // hash to the client -- just a boolean per row.
+    public static string? CurrentDeviceTokenHash(HttpRequest request)
+    {
+        var token = request.Cookies[AuthSessionOptions.TrustedDeviceCookieName];
+        return string.IsNullOrWhiteSpace(token) ? null : HashToken(token);
+    }
+
+    public static string HashToken(string token)
+    {
+        return Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(token.Trim()))).ToLowerInvariant();
+    }
+
+    private static readonly (string Needle, string Label)[] BrowserMarkers =
+    {
+        ("Edg/", "Edge"),
+        ("OPR/", "Opera"),
+        ("Chrome/", "Chrome"),
+        ("Firefox/", "Firefox"),
+        ("Safari/", "Safari"),
+    };
+
+    private static readonly (string Needle, string Label)[] OsMarkers =
+    {
+        ("Windows", "Windows"),
+        ("Mac OS X", "Mac"),
+        ("iPhone", "iOS"),
+        ("iPad", "iOS"),
+        ("Android", "Android"),
+        ("Linux", "Linux"),
+    };
+
+    // ponytail: substring sniffing, not a real UA parser -- this only feeds a display label in
+    // a security-settings list ("Chrome on Windows"), nothing security-relevant depends on it.
+    // Public: also reused by AppSessionIssuer for UserSession device labels.
+    public static string? DescribeUserAgent(string? userAgent)
+    {
+        if (string.IsNullOrWhiteSpace(userAgent)) return null;
+
+        var browser = BrowserMarkers.FirstOrDefault(m => userAgent.Contains(m.Needle, StringComparison.Ordinal)).Label;
+        var os = OsMarkers.FirstOrDefault(m => userAgent.Contains(m.Needle, StringComparison.Ordinal)).Label;
+
+        if (browser is null && os is null) return userAgent.Length > 80 ? userAgent[..80] : userAgent;
+        if (browser is null) return os;
+        if (os is null) return browser;
+        return $"{browser} on {os}";
+    }
+}

JobTrackerApi/Services/TwoFactorPendingTokenService.cs

@@ -0,0 +1,47 @@
+using System.Security.Cryptography;
+using Microsoft.Extensions.Caching.Memory;
+
+namespace JobTrackerApi.Services;
+
+public sealed record PendingTwoFactorSession(string UserId, bool RememberMe);
+
+public interface ITwoFactorPendingTokenService
+{
+    string IssuePendingToken(string userId, bool rememberMe);
+    PendingTwoFactorSession? Resolve(string pendingToken, bool consume);
+}
+
+// ponytail: server-side opaque token in IMemoryCache, deliberately NOT a JWT. A JWT signed
+// with the app's normal signing key would be accepted by the "local" JWT bearer auth scheme
+// for every other endpoint unless its issuer/audience/claims were carefully kept out of that
+// scheme's validation -- an opaque cache-backed token can never be presented as a bearer
+// token, so it structurally cannot grant a real session by itself. Single instance is fine:
+// this is a short-lived (5 min), single-process dev/prod deployment, same as the rest of this
+// app's in-memory state (rate limiter, IMemoryCache already registered in Program.cs).
+public sealed class TwoFactorPendingTokenService : ITwoFactorPendingTokenService
+{
+    private static readonly TimeSpan Ttl = TimeSpan.FromMinutes(5);
+    private readonly IMemoryCache _cache;
+
+    public TwoFactorPendingTokenService(IMemoryCache cache)
+    {
+        _cache = cache;
+    }
+
+    public string IssuePendingToken(string userId, bool rememberMe)
+    {
+        var token = Convert.ToHexString(RandomNumberGenerator.GetBytes(32)).ToLowerInvariant();
+        _cache.Set(CacheKey(token), new PendingTwoFactorSession(userId, rememberMe), Ttl);
+        return token;
+    }
+
+    public PendingTwoFactorSession? Resolve(string pendingToken, bool consume)
+    {
+        var key = CacheKey(pendingToken);
+        if (!_cache.TryGetValue(key, out PendingTwoFactorSession? session)) return null;
+        if (consume) _cache.Remove(key);
+        return session;
+    }
+
+    private static string CacheKey(string token) => $"2fa-pending:{token}";
+}