Issue #5: implement sqlite auth store and migrations

src/MxGateway.Server/Security/Authentication/AuthSqliteConnectionFactory.cs

@@ -0,0 +1,27 @@
+using Microsoft.Data.Sqlite;
+using Microsoft.Extensions.Options;
+using MxGateway.Server.Configuration;
+
+namespace MxGateway.Server.Security.Authentication;
+
+public sealed class AuthSqliteConnectionFactory(IOptions<GatewayOptions> options)
+{
+    public SqliteConnection CreateConnection()
+    {
+        string sqlitePath = options.Value.Authentication.SqlitePath;
+        string? directory = Path.GetDirectoryName(sqlitePath);
+
+        if (!string.IsNullOrWhiteSpace(directory))
+        {
+            Directory.CreateDirectory(directory);
+        }
+
+        SqliteConnectionStringBuilder builder = new()
+        {
+            DataSource = sqlitePath,
+            Mode = SqliteOpenMode.ReadWriteCreate
+        };
+
+        return new SqliteConnection(builder.ToString());
+    }
+}