Validate login request and refactor login handling

RecNet.Domain/Configuration/ServerConfig.cs

@@ -0,0 +1,24 @@
+using RecNet.Domain.Exceptions;
+
+namespace RecNet.Domain.Entities.Configuration;
+
+public class ServerConfig
+{
+    private ServerConfig(string key, string value)
+    {
+        Key = RequireValue(key, nameof(key));
+        Value = value;
+    }
+
+    public string Key { get; private set; }
+    public string Value { get; private set; }
+
+    public static ServerConfig Create(string key, string value)
+        => new(key, value);
+
+    public void SetValue(string value)
+        => Value = value;
+
+    private static string RequireValue(string value, string parameterName)
+        => !string.IsNullOrWhiteSpace(value) ? value : throw new DomainException($"{parameterName} is required.");
+}