GH-304: Added `Remove` and `RemoveAll` methods to SecureStorage (#330)

* [secure-storage] Added `Remove` and `RemoveAll`

* [secure-storage] Added tests for Remove/RemoveAll

* [secure-storage] Remove unnecessary method

We no longer consider the `SecAccessible` value when _retrieving_  KeyChain records anymore, so it’s unnecessary to pass this value into the Get call, and unnecessary to have a platform specific overload with this parameter for getting a record.

* [secure-storage] updated docs

* [secure-storage] update sample with remove methods

* [secure-storage] Fix GetAsync call for iOS

We don’t use the overload with SecAccessible any longer.

* Fix android remove, we must do a md5hash of the key as that is how it was stored :)

* [secure-storage] Fix iOS PlatformGet

DeviceTests/DeviceTests.Shared/SecureStorage_Tests.cs

@@ -19,7 +19,7 @@ namespace DeviceTests
             // Try the new platform specific api
             await SecureStorage.SetAsync(key, data, Security.SecAccessible.AfterFirstUnlock);
 
-            var b = await SecureStorage.GetAsync(key, Security.SecAccessible.AfterFirstUnlock);
+            var b = await SecureStorage.GetAsync(key);
 
             Assert.Equal(data, b);
 #endif
@@ -47,5 +47,43 @@ namespace DeviceTests
 
             Assert.Null(v);
         }
+
+        [Theory]
+        [InlineData("KEY_TO_REMOVE1", true)]
+        [InlineData("KEY_TO_REMOVE2", false)]
+        public async Task Remove_Key(string key, bool emulatePreApi23)
+        {
+#if __ANDROID__
+            SecureStorage.AlwaysUseAsymmetricKeyStorage = emulatePreApi23;
+#endif
+            await SecureStorage.SetAsync(key, "Irrelevant Data");
+
+            SecureStorage.Remove(key);
+
+            var v = await SecureStorage.GetAsync(key);
+
+            Assert.Null(v);
+        }
+
+        [Theory]
+        [InlineData(true, new[] { "KEYS_TO_REMOVEA1", "KEYS_TO_REMOVEA2" })]
+        [InlineData(false, new[] { "KEYS_TO_REMOVEB1", "KEYS_TO_REMOVEB2" })]
+        public async Task Remove_All_Keys(bool emulatePreApi23, string[] keys)
+        {
+#if __ANDROID__
+            SecureStorage.AlwaysUseAsymmetricKeyStorage = emulatePreApi23;
+#endif
+
+            // Set a couple keys
+            foreach (var key in keys)
+                await SecureStorage.SetAsync(key, "Irrelevant Data");
+
+            // Remove them all
+            SecureStorage.RemoveAll();
+
+            // Make sure they are all removed
+            foreach (var key in keys)
+                Assert.Null(await SecureStorage.GetAsync(key));
+        }
     }
 }

Samples/Samples/View/SecureStoragePage.xaml

@@ -21,6 +21,9 @@
 
                 <Button Text="Load" Command="{Binding LoadCommand}" IsEnabled="{Binding IsNotBusy}" />
                 <Button Text="Save" Command="{Binding SaveCommand}" IsEnabled="{Binding IsNotBusy}" />
+                <Button Text="Remove" Command="{Binding RemoveCommand}" IsEnabled="{Binding IsNotBusy}" />
+
+                <Button Text="Remove All" Command="{Binding RemoveAllCommand}" IsEnabled="{Binding IsNotBusy}" Margin="0,10,0,0" />
             </StackLayout>
         </ScrollView>
     </StackLayout>

Samples/Samples/ViewModel/SecureStorageViewModel.cs

@@ -14,6 +14,8 @@ namespace Samples.ViewModel
         {
             LoadCommand = new Command(OnLoad);
             SaveCommand = new Command(OnSave);
+            RemoveCommand = new Command(OnRemove);
+            RemoveAllCommand = new Command(OnRemoveAll);
         }
 
         public string Key
@@ -32,6 +34,10 @@ namespace Samples.ViewModel
 
         public ICommand SaveCommand { get; }
 
+        public ICommand RemoveCommand { get; }
+
+        public ICommand RemoveAllCommand { get; }
+
         async void OnLoad()
         {
             if (IsBusy)
@@ -66,5 +72,39 @@ namespace Samples.ViewModel
             }
             IsBusy = false;
         }
+
+        async void OnRemove()
+        {
+            if (IsBusy)
+                return;
+            IsBusy = true;
+
+            try
+            {
+                SecureStorage.Remove(Key);
+            }
+            catch (Exception ex)
+            {
+                await DisplayAlertAsync(ex.Message);
+            }
+            IsBusy = false;
+        }
+
+        async void OnRemoveAll()
+        {
+            if (IsBusy)
+                return;
+            IsBusy = true;
+
+            try
+            {
+                SecureStorage.RemoveAll();
+            }
+            catch (Exception ex)
+            {
+                await DisplayAlertAsync(ex.Message);
+            }
+            IsBusy = false;
+        }
     }
 }

Xamarin.Essentials/SecureStorage/SecureStorage.android.cs

@@ -51,6 +51,42 @@ namespace Xamarin.Essentials
             return Task.CompletedTask;
         }
 
+        static bool PlatformRemove(string key)
+        {
+            var context = Platform.AppContext;
+
+            key = Utils.Md5Hash(key);
+
+            using (var prefs = context.GetSharedPreferences(Alias, FileCreationMode.Private))
+            {
+                if (prefs.Contains(key))
+                {
+                    using (var prefsEditor = prefs.Edit())
+                    {
+                        prefsEditor.Remove(key);
+                        prefsEditor.Commit();
+                        return true;
+                    }
+                }
+            }
+
+            return false;
+        }
+
+        static void PlatformRemoveAll()
+        {
+            var context = Platform.AppContext;
+
+            using (var prefs = context.GetSharedPreferences(Alias, FileCreationMode.Private))
+            using (var prefsEditor = prefs.Edit())
+            {
+                foreach (var key in prefs.All.Keys)
+                    prefsEditor.Remove(key);
+
+                prefsEditor.Commit();
+            }
+        }
+
         internal static bool AlwaysUseAsymmetricKeyStorage { get; set; } = false;
     }
 

Xamarin.Essentials/SecureStorage/SecureStorage.ios.cs

@@ -11,16 +11,6 @@ namespace Xamarin.Essentials
         public static SecAccessible DefaultAccessible { get; set; } =
             SecAccessible.AfterFirstUnlock;
 
-        public static Task<string> GetAsync(string key, SecAccessible accessible)
-        {
-            if (string.IsNullOrWhiteSpace(key))
-                throw new ArgumentNullException(nameof(key));
-
-            var kc = new KeyChain(accessible);
-
-            return Task.FromResult(kc.ValueForKey(key, Alias));
-        }
-
         public static Task SetAsync(string key, string value, SecAccessible accessible)
         {
             if (string.IsNullOrWhiteSpace(key))
@@ -35,11 +25,33 @@ namespace Xamarin.Essentials
             return Task.CompletedTask;
         }
 
-        static Task<string> PlatformGetAsync(string key) =>
-            GetAsync(key, DefaultAccessible);
+        static Task<string> PlatformGetAsync(string key)
+        {
+            if (string.IsNullOrWhiteSpace(key))
+                throw new ArgumentNullException(nameof(key));
+
+            var kc = new KeyChain(DefaultAccessible);
+            var value = kc.ValueForKey(key, Alias);
+
+            return Task.FromResult(value);
+        }
 
         static Task PlatformSetAsync(string key, string data) =>
             SetAsync(key, data, DefaultAccessible);
+
+        static bool PlatformRemove(string key)
+        {
+            var kc = new KeyChain(DefaultAccessible);
+
+            return kc.Remove(key, Alias);
+        }
+
+        static void PlatformRemoveAll()
+        {
+            var kc = new KeyChain(DefaultAccessible);
+
+            kc.RemoveAll(Alias);
+        }
     }
 
     class KeyChain
@@ -89,6 +101,30 @@ namespace Xamarin.Essentials
                 throw new Exception($"Error adding record: {result}");
         }
 
+        internal bool Remove(string key, string service)
+        {
+            var record = ExistingRecordForKey(key, service);
+            var match = SecKeyChain.QueryAsRecord(record, out var resultCode);
+
+            if (resultCode == SecStatusCode.Success)
+            {
+                RemoveRecord(record);
+                return true;
+            }
+
+            return false;
+        }
+
+        internal void RemoveAll(string service)
+        {
+            var query = new SecRecord(SecKind.GenericPassword)
+            {
+                Service = service
+            };
+
+            SecKeyChain.Remove(query);
+        }
+
         SecRecord CreateRecordForNewKeyValue(string key, string value, string service)
         {
             return new SecRecord(SecKind.GenericPassword)

Xamarin.Essentials/SecureStorage/SecureStorage.netstandard.cs

@@ -9,5 +9,11 @@ namespace Xamarin.Essentials
 
         static Task PlatformSetAsync(string key, string data) =>
             throw new NotImplementedInReferenceAssemblyException();
+
+        static bool PlatformRemove(string key) =>
+            throw new NotImplementedInReferenceAssemblyException();
+
+        static void PlatformRemoveAll() =>
+            throw new NotImplementedInReferenceAssemblyException();
     }
 }

Xamarin.Essentials/SecureStorage/SecureStorage.shared.cs

@@ -25,5 +25,11 @@ namespace Xamarin.Essentials
 
             return PlatformSetAsync(key, value);
         }
+
+        public static bool Remove(string key)
+            => PlatformRemove(key);
+
+        public static void RemoveAll()
+            => PlatformRemoveAll();
     }
 }

Xamarin.Essentials/SecureStorage/SecureStorage.uwp.cs

@@ -41,6 +41,26 @@ namespace Xamarin.Essentials
             settings.Values[key] = encBytes;
         }
 
+        static bool PlatformRemove(string key)
+        {
+            var settings = GetSettings(Alias);
+
+            if (settings.Values.ContainsKey(key))
+            {
+                settings.Values.Remove(key);
+                return true;
+            }
+
+            return false;
+        }
+
+        static void PlatformRemoveAll()
+        {
+            var settings = GetSettings(Alias);
+
+            settings.Values.Clear();
+        }
+
         static ApplicationDataContainer GetSettings(string name)
         {
             var localSettings = ApplicationData.Current.LocalSettings;

docs/en/FrameworksIndex/xamarin-essentials-android.xml

@@ -375,6 +375,8 @@
     </Type>
     <Type Name="Xamarin.Essentials.SecureStorage" Id="T:Xamarin.Essentials.SecureStorage">
       <Member Id="M:Xamarin.Essentials.SecureStorage.GetAsync(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.Remove(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.RemoveAll" />
       <Member Id="M:Xamarin.Essentials.SecureStorage.SetAsync(System.String,System.String)" />
     </Type>
     <Type Name="Xamarin.Essentials.SensorSpeed" Id="T:Xamarin.Essentials.SensorSpeed">

docs/en/FrameworksIndex/xamarin-essentials-ios.xml

@@ -372,7 +372,8 @@
     </Type>
     <Type Name="Xamarin.Essentials.SecureStorage" Id="T:Xamarin.Essentials.SecureStorage">
       <Member Id="M:Xamarin.Essentials.SecureStorage.GetAsync(System.String)" />
-      <Member Id="M:Xamarin.Essentials.SecureStorage.GetAsync(System.String,Security.SecAccessible)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.Remove(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.RemoveAll" />
       <Member Id="M:Xamarin.Essentials.SecureStorage.SetAsync(System.String,System.String)" />
       <Member Id="M:Xamarin.Essentials.SecureStorage.SetAsync(System.String,System.String,Security.SecAccessible)" />
       <Member Id="P:Xamarin.Essentials.SecureStorage.DefaultAccessible" />

docs/en/FrameworksIndex/xamarin-essentials-uwp.xml

@@ -371,6 +371,8 @@
     </Type>
     <Type Name="Xamarin.Essentials.SecureStorage" Id="T:Xamarin.Essentials.SecureStorage">
       <Member Id="M:Xamarin.Essentials.SecureStorage.GetAsync(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.Remove(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.RemoveAll" />
       <Member Id="M:Xamarin.Essentials.SecureStorage.SetAsync(System.String,System.String)" />
     </Type>
     <Type Name="Xamarin.Essentials.SensorSpeed" Id="T:Xamarin.Essentials.SensorSpeed">

docs/en/FrameworksIndex/xamarin-essentials.xml

@@ -371,6 +371,8 @@
     </Type>
     <Type Name="Xamarin.Essentials.SecureStorage" Id="T:Xamarin.Essentials.SecureStorage">
       <Member Id="M:Xamarin.Essentials.SecureStorage.GetAsync(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.Remove(System.String)" />
+      <Member Id="M:Xamarin.Essentials.SecureStorage.RemoveAll" />
       <Member Id="M:Xamarin.Essentials.SecureStorage.SetAsync(System.String,System.String)" />
     </Type>
     <Type Name="Xamarin.Essentials.SensorSpeed" Id="T:Xamarin.Essentials.SensorSpeed">

docs/en/Xamarin.Essentials/SecureStorage.xml

@@ -71,30 +71,44 @@
         </remarks>
       </Docs>
     </Member>
-    <Member MemberName="GetAsync">
-      <MemberSignature Language="C#" Value="public static System.Threading.Tasks.Task&lt;string&gt; GetAsync (string key, Security.SecAccessible accessible);" />
-      <MemberSignature Language="ILAsm" Value=".method public static hidebysig class System.Threading.Tasks.Task`1&lt;string&gt; GetAsync(string key, valuetype Security.SecAccessible accessible) cil managed" />
-      <MemberSignature Language="DocId" Value="M:Xamarin.Essentials.SecureStorage.GetAsync(System.String,Security.SecAccessible)" />
+    <Member MemberName="Remove">
+      <MemberSignature Language="C#" Value="public static bool Remove (string key);" />
+      <MemberSignature Language="ILAsm" Value=".method public static hidebysig bool Remove(string key) cil managed" />
+      <MemberSignature Language="DocId" Value="M:Xamarin.Essentials.SecureStorage.Remove(System.String)" />
       <MemberType>Method</MemberType>
       <AssemblyInfo>
         <AssemblyName>Xamarin.Essentials</AssemblyName>
         <AssemblyVersion>1.0.0.0</AssemblyVersion>
       </AssemblyInfo>
       <ReturnValue>
-        <ReturnType>System.Threading.Tasks.Task&lt;System.String&gt;</ReturnType>
+        <ReturnType>System.Boolean</ReturnType>
       </ReturnValue>
       <Parameters>
         <Parameter Name="key" Type="System.String" />
-        <Parameter Name="accessible" Type="Security.SecAccessible" />
       </Parameters>
       <Docs>
-        <param name="key">Storage Key.</param>
-        <param name="accessible">SecAccessible for iOS to use</param>
-        <summary>Gets the decrypted value for a given Key. iOS override to specify SecAccessible for the KeyChain.</summary>
-        <returns>
-          <para></para>
-        </returns>
-        <remarks>iOS: Default SecAccessible to use for all Get/Set calls to KeyChain. Default value is AfterFirstUnlock.</remarks>
+        <param name="key">The key to remove.</param>
+        <summary>Removes the encrypted key/value pair for the given key.</summary>
+        <returns>Returns true if the key value pair was removed.</returns>
+        <remarks></remarks>
+      </Docs>
+    </Member>
+    <Member MemberName="RemoveAll">
+      <MemberSignature Language="C#" Value="public static void RemoveAll ();" />
+      <MemberSignature Language="ILAsm" Value=".method public static hidebysig void RemoveAll() cil managed" />
+      <MemberSignature Language="DocId" Value="M:Xamarin.Essentials.SecureStorage.RemoveAll" />
+      <MemberType>Method</MemberType>
+      <AssemblyInfo>
+        <AssemblyName>Xamarin.Essentials</AssemblyName>
+        <AssemblyVersion>1.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>System.Void</ReturnType>
+      </ReturnValue>
+      <Parameters />
+      <Docs>
+        <summary>Removes all of the stored encrypted key/value pairs.</summary>
+        <remarks></remarks>
       </Docs>
     </Member>
     <Member MemberName="SetAsync">
@@ -145,7 +159,7 @@
       <Docs>
         <param name="key">Storage Key.</param>
         <param name="value">The value to be encrypted.</param>
-        <param name="accessible">To be added.</param>
+        <param name="accessible">The KeyChain accessibility to create the encrypted record with.</param>
         <summary>Stores the value which is encrypted, for a given Key. iOS override to specify SecAccessible for the KeyChain.</summary>
         <returns>
           <para></para>