feat(backend): start authentication controllers

Foxnouns.Backend/Services/KeyCacheService.cs

@@ -0,0 +1,51 @@
+using Foxnouns.Backend.Database;
+using Foxnouns.Backend.Database.Models;
+using Foxnouns.Backend.Utils;
+using Microsoft.EntityFrameworkCore;
+using NodaTime;
+
+namespace Foxnouns.Backend.Services;
+
+public class KeyCacheService(DatabaseContext db, IClock clock, ILogger logger)
+{
+    public Task SetKeyAsync(string key, string value, Duration expireAfter) =>
+        db.SetKeyAsync(key, value, clock.GetCurrentInstant() + expireAfter);
+
+    public async Task SetKeyAsync(string key, string value, Instant expires)
+    {
+        db.TemporaryKeys.Add(new TemporaryKey
+        {
+            Expires = expires,
+            Key = key,
+            Value = value,
+        });
+        await db.SaveChangesAsync();
+    }
+
+    public async Task<string?> GetKeyAsync(string key, bool delete = false)
+    {
+        var value = await db.TemporaryKeys.FirstOrDefaultAsync(k => k.Key == key);
+        if (value == null) return null;
+
+        if (delete)
+        {
+            await db.TemporaryKeys.Where(k => k.Key == key).ExecuteDeleteAsync();
+            await db.SaveChangesAsync();
+        }
+
+        return value.Value;
+    }
+
+    public async Task DeleteExpiredKeysAsync()
+    {
+        var count = await db.TemporaryKeys.Where(k => k.Expires < clock.GetCurrentInstant()).ExecuteDeleteAsync();
+        if (count != 0) logger.Information("Removed {Count} expired keys from the database", count);
+    }
+
+    public async Task<string> GenerateAuthStateAsync()
+    {
+        var state = OauthUtils.RandomToken();
+        await SetKeyAsync($"oauth_state:{state}", "", Duration.FromMinutes(10));
+        return state;
+    }
+}