move some xamarin specific services to app proj

src/App/Services/SecureStorageService.cs

@@ -0,0 +1,56 @@
+using Bit.Core.Abstractions;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Serialization;
+using System.Threading.Tasks;
+
+namespace Bit.App.Services
+{
+    public class SecureStorageService : IStorageService
+    {
+        private readonly string _keyFormat = "bwSecureStorage:{0}";
+        private readonly JsonSerializerSettings _jsonSettings = new JsonSerializerSettings
+        {
+            ContractResolver = new CamelCasePropertyNamesContractResolver()
+        };
+
+        public async Task<T> GetAsync<T>(string key)
+        {
+            var formattedKey = string.Format(_keyFormat, key);
+            var val = await Xamarin.Essentials.SecureStorage.GetAsync(formattedKey);
+            if(typeof(T) == typeof(string))
+            {
+                return (T)(object)val;
+            }
+            else
+            {
+                return JsonConvert.DeserializeObject<T>(val, _jsonSettings);
+            }
+        }
+
+        public async Task SaveAsync<T>(string key, T obj)
+        {
+            if(obj == null)
+            {
+                await RemoveAsync(key);
+                return;
+            }
+            var formattedKey = string.Format(_keyFormat, key);
+            if(typeof(T) == typeof(string))
+            {
+                await Xamarin.Essentials.SecureStorage.SetAsync(formattedKey, obj as string);
+            }
+            else
+            {
+                await Xamarin.Essentials.SecureStorage.SetAsync(formattedKey,
+                    JsonConvert.SerializeObject(obj, _jsonSettings));
+            }
+        }
+
+        public Task RemoveAsync(string key)
+        {
+            var formattedKey = string.Format(_keyFormat, key);
+            Xamarin.Essentials.SecureStorage.Remove(formattedKey);
+            return Task.FromResult(0);
+        }
+    }
+}