Implemented complete oauth2 flow with modular providers

The local oauth2 provider still needs A LOT of love. But the general oauth2 workflow works. The http api client needs an option to disable the authentication things and we need to switch to the local storage for storing access, refresh and timestamp for the client

Moonlight.ApiServer/Implementations/OAuth2/LocalOAuth2Provider.cs

@@ -0,0 +1,60 @@
+using MoonCore.Extended.Abstractions;
+using MoonCore.Extensions;
+using MoonCore.Services;
+using Moonlight.ApiServer.Configuration;
+using Moonlight.ApiServer.Database.Entities;
+using Moonlight.ApiServer.Interfaces.OAuth2;
+using Moonlight.Shared.Http.Responses.OAuth2;
+
+namespace Moonlight.ApiServer.Implementations.OAuth2;
+
+public class LocalOAuth2Provider : IOAuth2Provider
+{
+    public async Task<User?> Sync(IServiceProvider provider, string accessToken)
+    {
+        var logger = provider.GetRequiredService<ILogger<LocalOAuth2Provider>>();
+        
+        try
+        {
+            var configService = provider.GetRequiredService<ConfigService<AppConfiguration>>();
+            var config = configService.Get();
+
+            using var httpClient = new HttpClient();
+            
+            httpClient.DefaultRequestHeaders.Add("Authorization", accessToken);
+            
+            var response = await httpClient.GetAsync($"{config.PublicUrl}/oauth2/info");
+            await response.HandlePossibleApiError();
+            var info = await response.ParseAsJson<InfoResponse>();
+
+            var userRepo = provider.GetRequiredService<DatabaseRepository<User>>();
+            var user = userRepo.Get().FirstOrDefault(x => x.Email == info.Email);
+
+            if (user == null) // User not found, register a new one
+            {
+                user = userRepo.Add(new User()
+                {
+                    Email = info.Email,
+                    Username = info.Username
+                });
+            }
+            else if (user.Username != info.Username) // Username updated?
+            {
+                // Username not used by another user?
+                if (!userRepo.Get().Any(x => x.Username == info.Username))
+                {
+                    // Update username
+                    user.Username = info.Username;
+                    userRepo.Update(user);
+                }
+            }
+
+            return user;
+        }
+        catch (Exception e)
+        {
+            logger.LogCritical("Unable to sync user: {e}", e);
+            return null;
+        }
+    }
+}