Added a preprocessor script

Assets/Scripts/GoogleSignInIOSBuildPatch.cs

@@ -0,0 +1,63 @@
+#if UNITY_IOS
+using System.IO;
+using UnityEditor;
+using UnityEditor.Callbacks;
+using UnityEditor.iOS.Xcode;
+using UnityEngine;
+
+public class GoogleSignInIOSBuildPatch
+{
+    [PostProcessBuild(100)]
+    public static void OnPostProcessBuild(BuildTarget buildTarget, string pathToBuiltProject)
+    {
+        if (buildTarget != BuildTarget.iOS) return;
+
+        string plistPath = Path.Combine(pathToBuiltProject, "Info.plist");
+
+        // === Modify Info.plist ===
+        PlistDocument plist = new PlistDocument();
+        plist.ReadFromFile(plistPath);
+        PlistElementDict rootDict = plist.root;
+
+        // 1. Add GIDClientID
+        rootDict.SetString("GIDClientID", GameConstants.iOS_ClientID);
+
+        // 2. Add custom URL scheme
+        PlistElementArray urlTypes = rootDict.CreateArray("CFBundleURLTypes");
+        PlistElementDict urlDict = urlTypes.AddDict();
+        PlistElementArray schemes = urlDict.CreateArray("CFBundleURLSchemes");
+        schemes.AddString(GameConstants.iOS_URL_Scheme);
+
+        plist.WriteToFile(plistPath);
+        Debug.Log("✅ Info.plist patched with GIDClientID and CFBundleURLSchemes.");
+
+        // === Modify UnityAppController.mm ===
+        string appControllerPath = Path.Combine(pathToBuiltProject, "Classes", "UnityAppController.mm");
+        if (!File.Exists(appControllerPath))
+        {
+            Debug.LogWarning("⚠️ UnityAppController.mm not found. Skipping patch.");
+            return;
+        }
+
+        string content = File.ReadAllText(appControllerPath);
+        string injection = $"[GIDSignIn sharedInstance].clientID = @\"{GameConstants.iOS_ClientID}\";";
+
+        if (!content.Contains(injection))
+        {
+            string marker = "didFinishLaunchingWithOptions:(NSDictionary*)launchOptions";
+            int index = content.IndexOf(marker);
+            if (index > -1)
+            {
+                int insertAfter = content.IndexOf("{", index) + 1;
+                content = content.Insert(insertAfter, "\n    " + injection);
+                File.WriteAllText(appControllerPath, content);
+                Debug.Log("✅ UnityAppController.mm patched with GIDClientID.");
+            }
+            else
+            {
+                Debug.LogWarning("⚠️ didFinishLaunchingWithOptions not found in UnityAppController.mm");
+            }
+        }
+    }
+}
+#endif

Assets/Scripts/GoogleSignInIOSBuildPatch.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 74a4088da3768004389d6516bc9a559a
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: