store previous key and userid so we can determine if stored crypto is usable before a sync

src/App/Abstractions/Services/IAuthService.cs

@@ -9,6 +9,8 @@ namespace Bit.App.Abstractions
         bool IsAuthenticatedTwoFactor { get; }
         string Token { get; set; }
         string UserId { get; set; }
+        string PreviousUserId { get; }
+        bool UserIdChanged { get; }
         string Email { get; set; }
         string PIN { get; set; }
 

src/App/Abstractions/Services/ICryptoService.cs

@@ -6,6 +6,8 @@ namespace Bit.App.Abstractions
     {
         string Base64Key { get; }
         byte[] Key { get; set; }
+        byte[] PreviousKey { get; }
+        bool KeyChanged { get; }
 
         string Decrypt(CipherString encyptedValue);
         CipherString Encrypt(string plaintextValue);

src/App/Pages/Tools/ToolsExtensionPage.cs

@@ -161,7 +161,11 @@ namespace Bit.App.Pages
             var activatedButton = new Button
             {
                 Text = "See Supported Apps",
-                Command = new Command(() => Device.OpenUri(new Uri("https://bitwarden.com"))),
+                Command = new Command(() =>
+                {
+                    _googleAnalyticsService.TrackAppEvent("SeeSupportedApps");
+                    Device.OpenUri(new Uri("https://bitwarden.com"));
+                }),
                 VerticalOptions = LayoutOptions.End,
                 HorizontalOptions = LayoutOptions.Fill,
                 Style = (Style)Application.Current.Resources["btn-primary"]

src/App/Services/AuthService.cs

@@ -12,6 +12,7 @@ namespace Bit.App.Services
         private const string TokenKey = "token";
         private const string EmailKey = "email";
         private const string UserIdKey = "userId";
+        private const string PreviousUserIdKey = "previousUserId";
         private const string PinKey = "pin";
 
         private readonly ISecureStorageService _secureStorage;
@@ -22,6 +23,7 @@ namespace Bit.App.Services
         private string _token;
         private string _email;
         private string _userId;
+        private string _previousUserId;
         private string _pin;
 
         public AuthService(
@@ -90,6 +92,7 @@ namespace Bit.App.Services
                 }
                 else
                 {
+                    PreviousUserId = _userId;
                     _settings.Remove(UserIdKey);
                 }
 
@@ -97,6 +100,30 @@ namespace Bit.App.Services
             }
         }
 
+        public string PreviousUserId
+        {
+            get
+            {
+                if(_previousUserId != null)
+                {
+                    return _previousUserId;
+                }
+
+                _previousUserId = _settings.GetValueOrDefault<string>(PreviousUserIdKey);
+                return _previousUserId;
+            }
+            private set
+            {
+                if(value != null)
+                {
+                    _settings.AddOrUpdateValue(PreviousUserIdKey, value);
+                    _previousUserId = value;
+                }
+            }
+        }
+
+        public bool UserIdChanged => PreviousUserId != UserId;
+
         public string Email
         {
             get

src/App/Services/CryptoService.cs

@@ -4,18 +4,21 @@ using System.Text;
 using Bit.App.Abstractions;
 using Bit.App.Models;
 using PCLCrypto;
+using System.Linq;
 
 namespace Bit.App.Services
 {
     public class CryptoService : ICryptoService
     {
         private const string KeyKey = "key";
+        private const string PreviousKeyKey = "previousKey";
         private const int InitializationVectorSize = 16;
 
         private readonly Random _random = new Random();
         private readonly ISecureStorageService _secureStorage;
         private readonly IKeyDerivationService _keyDerivationService;
         private byte[] _key;
+        private byte[] _previousKey;
 
         public CryptoService(
             ISecureStorageService secureStorage,
@@ -44,6 +47,7 @@ namespace Bit.App.Services
                 }
                 else
                 {
+                    PreviousKey = _key;
                     _secureStorage.Delete(KeyKey);
                     _key = null;
                 }
@@ -63,6 +67,29 @@ namespace Bit.App.Services
             }
         }
 
+        public byte[] PreviousKey
+        {
+            get
+            {
+                if(_previousKey == null)
+                {
+                    _previousKey = _secureStorage.Retrieve(PreviousKeyKey);
+                }
+
+                return _previousKey;
+            }
+            private set
+            {
+                if(value != null)
+                {
+                    _secureStorage.Store(PreviousKeyKey, value);
+                    _previousKey = value;
+                }
+            }
+        }
+
+        public bool KeyChanged => !PreviousKey?.SequenceEqual(Key) ?? Key == null ? false : true;
+
         public CipherString Encrypt(string plaintextValue)
         {
             if(Key == null)