[PM-22739] Add ClaimsPrincipal Extension

feat: add ClaimsPrincipal Extension
test: add tests

src/Core/Auth/UserFeatures/SendAccess/SendAccessClaimsPrincipalExtensions.cs

@@ -0,0 +1,22 @@
+using System.Security.Claims;
+using Bit.Core.Identity;
+
+namespace Bit.Core.Auth.UserFeatures.SendAccess;
+
+public static class SendAccessClaimsPrincipalExtensions
+{
+    public static Guid GetSendId(this ClaimsPrincipal user)
+    {
+        ArgumentNullException.ThrowIfNull(user);
+
+        var sendIdClaim = user.FindFirst(Claims.SendId)
+            ?? throw new InvalidOperationException("Send ID claim not found.");
+
+        if (!Guid.TryParse(sendIdClaim.Value, out var sendGuid))
+        {
+            throw new InvalidOperationException("Invalid Send ID claim value.");
+        }
+
+        return sendGuid;
+    }
+}