Fix the "clearing passwords in 45s" function

- Copied passwords in the extension are not cleaned.

pass/Controllers/PasswordDetailTableViewController.swift

@@ -391,7 +391,7 @@ class PasswordDetailTableViewController: UITableViewController, UIGestureRecogni
         
         // copy HOTP to pasteboard (will update counter)
         if let plainPassword = password!.getNextHotp() {
-            Utils.copyToPasteboard(textToCopy: plainPassword)
+            SecurePasteboard.shared.copy(textToCopy: plainPassword)
         }
         
         // commit the change of HOTP counter
@@ -413,7 +413,7 @@ class PasswordDetailTableViewController: UITableViewController, UIGestureRecogni
             }
             return;
         }
-        Utils.copyToPasteboard(textToCopy: password?.password)
+        SecurePasteboard.shared.copy(textToCopy: password?.password)
         UIApplication.shared.open(url, options: [:], completionHandler: nil)
     }
 
@@ -480,7 +480,7 @@ class PasswordDetailTableViewController: UITableViewController, UIGestureRecogni
     
     override func tableView(_ tableView: UITableView, performAction action: Selector, forRowAt indexPath: IndexPath, withSender sender: Any?) {
         if action == #selector(copy(_:)) {
-            Utils.copyToPasteboard(textToCopy: tableData[indexPath.section].item[indexPath.row].content)
+            SecurePasteboard.shared.copy(textToCopy: tableData[indexPath.section].item[indexPath.row].content)
         }
     }
     

pass/Controllers/PasswordEditorTableViewController.swift

@@ -189,7 +189,7 @@ class PasswordEditorTableViewController: UITableViewController, FillPasswordTabl
         }
         let length = passwordLengthCell?.roundedValue ?? 0
         let plainPassword = Utils.generatePassword(length: length)
-        Utils.copyToPasteboard(textToCopy: plainPassword)
+        SecurePasteboard.shared.copy(textToCopy: plainPassword)
         
         // update tableData so to make sure reloadData() works correctly
         tableData[passwordSection][0][PasswordEditorCellKey.content] = plainPassword

pass/Controllers/PasswordsViewController.swift

@@ -370,7 +370,7 @@ class PasswordsViewController: UIViewController, UITableViewDataSource, UITableV
             do {
                 decryptedPassword = try self.passwordStore.decrypt(passwordEntity: passwordEntity, requestPGPKeyPassphrase: self.requestPGPKeyPassphrase)
                 DispatchQueue.main.async {
-                    Utils.copyToPasteboard(textToCopy: decryptedPassword?.password)
+                    SecurePasteboard.shared.copy(textToCopy: decryptedPassword?.password)
                     SVProgressHUD.showSuccess(withStatus: "Password copied, and will be cleared in 45 seconds.")
                     SVProgressHUD.dismiss(withDelay: 0.6)
                 }

pass/Helpers/SecurePasteboard.swift

@@ -0,0 +1,55 @@
+//
+//  SecurePasteboard.swift
+//  pass
+//
+//  Created by Yishi Lin on 2017/7/27.
+//  Copyright © 2017 Bob Sun. All rights reserved.
+//
+
+import Foundation
+import UIKit
+
+class SecurePasteboard {
+    public static let shared = SecurePasteboard()
+    private var backgroundTaskID: UIBackgroundTaskIdentifier? = nil
+    
+    func copy(textToCopy: String?, expirationTime: Double = 45) {
+        // copy to the pasteboard
+        UIPasteboard.general.string = textToCopy ?? ""
+        
+        // clean the pasteboard after expirationTime
+        guard expirationTime > 0 else {
+            return
+        }
+        
+        // exit the existing background task, if any
+        if let backgroundTaskID = backgroundTaskID {
+            UIApplication.shared.endBackgroundTask(backgroundTaskID)
+            self.backgroundTaskID = nil
+        }
+        
+        backgroundTaskID = UIApplication.shared.beginBackgroundTask(expirationHandler: { [weak self] in
+            guard let taskID = self?.backgroundTaskID else {
+                return
+            }
+            if textToCopy == UIPasteboard.general.string {
+                UIPasteboard.general.string = ""
+            }
+            UIApplication.shared.endBackgroundTask(taskID)
+        })
+        
+        DispatchQueue.global(qos: .utility).asyncAfter(deadline: .now() + expirationTime) { [weak self] in
+            guard let strongSelf = self else {
+                return
+            }
+            if textToCopy == UIPasteboard.general.string {
+                UIPasteboard.general.string = ""
+            }
+            if let backgroundTaskID = strongSelf.backgroundTaskID {
+                UIApplication.shared.endBackgroundTask(backgroundTaskID)
+                strongSelf.backgroundTaskID = nil
+            }
+        }
+    }
+    
+}

pass/Views/LabelTableViewCell.swift

@@ -101,7 +101,7 @@ class LabelTableViewCell: UITableViewCell {
     }
 
     override func copy(_ sender: Any?) {
-        Utils.copyToPasteboard(textToCopy: cellData?.content)
+        SecurePasteboard.shared.copy(textToCopy: cellData?.content)
     }
         
     func revealPassword(_ sender: Any?) {