Implemented Core client

Cloudflare/Interfaces/IAuthentication.cs

@@ -0,0 +1,16 @@
+using System.Net.Http;
+
+namespace AMWD.Net.Api.Cloudflare.Auth
+{
+	/// <summary>
+	/// Defines the interface to add authentication information.
+	/// </summary>
+	public interface IAuthentication
+	{
+		/// <summary>
+		/// Adds authentication headers to the given <see cref="HttpClient"/>.
+		/// </summary>
+		/// <param name="httpClient">The <see cref="HttpClient"/> to add the headers to.</param>
+		void AddHeader(HttpClient httpClient);
+	}
+}