feat: add request validation

src/request.validation/Problem.cs

@@ -0,0 +1,35 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Validation;
+
+/// <summary>
+/// Represents a validation problem identified during a request validation process.
+/// </summary>
+public record Problem
+{
+	/// <summary>
+	/// The name of the property.
+	/// </summary>
+	public required string PropertyName { get; init; }
+
+	/// <summary>
+	/// Custom severity level associated with the failure.
+	/// </summary>
+	public Severity Severity { get; init; } = Severity.Error;
+
+	/// <summary>
+	/// The error message
+	/// </summary>
+	public required string Message { get; init; }
+
+	/// <summary>
+	/// Gets or sets the error code.
+	/// </summary>
+	public string? Code { get; init; }
+
+	/// <summary>
+	/// The property value that caused the failure.
+	/// </summary>
+	public object? AttemptedValue { get; init; }
+}