feat(AuthTokenKeys): Erstellt, um Parameter für Authentifizierungs-Tokens zu konfigurieren.

- AuthTokenKeys aus der Konfiguration in Program.cs lesen.
 - Upgrade von Core.Abstractions auf 3.5

EnvelopeGenerator.GeneratorAPI/Models/AuthTokenKeys.cs

@@ -0,0 +1,28 @@
+namespace EnvelopeGenerator.GeneratorAPI.Models;
+
+/// <summary>
+/// Represents the keys and default values used for authentication token handling 
+/// within the Envelope Generator API.
+/// </summary>
+public class AuthTokenKeys
+{
+    /// <summary>
+    /// Gets the name of the cookie used to store the authentication token.
+    /// </summary>
+    public string Cookie { get; init; } = "AuthToken";
+
+    /// <summary>
+    /// Gets the name of the query string parameter used to pass the authentication token.
+    /// </summary>
+    public string QueryString { get; init; } = "AuthToken";
+
+    /// <summary>
+    /// Gets the expected issuer value for the authentication token.
+    /// </summary>
+    public string Issuer { get; init; } = "auth.digitaldata.works";
+
+    /// <summary>
+    /// Gets the expected audience value for the authentication token.
+    /// </summary>
+    public string Audience { get; init; } = "sign-flow-gen.digitaldata.works";
+}