Add a core library and a class to retrieve todo items

src/Todo.CLI.sln

@@ -5,6 +5,8 @@ VisualStudioVersion = 16.0.29326.143
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Todo.CLI", "Todo.CLI\Todo.CLI.csproj", "{DAE1B155-3197-4C6A-A447-E042DE7185F3}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Todo.Core", "Todo.Core\Todo.Core.csproj", "{B0359C3C-B44F-4F18-9A7F-D879B7C368E4}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,6 +17,10 @@ Global
 		{DAE1B155-3197-4C6A-A447-E042DE7185F3}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{DAE1B155-3197-4C6A-A447-E042DE7185F3}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{DAE1B155-3197-4C6A-A447-E042DE7185F3}.Release|Any CPU.Build.0 = Release|Any CPU
+		{B0359C3C-B44F-4F18-9A7F-D879B7C368E4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B0359C3C-B44F-4F18-9A7F-D879B7C368E4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B0359C3C-B44F-4F18-9A7F-D879B7C368E4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{B0359C3C-B44F-4F18-9A7F-D879B7C368E4}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/Todo.Core/ITodoItemRetriever.cs

@@ -0,0 +1,13 @@
+using Microsoft.Graph;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Todo.Core
+{
+    public interface ITodoItemRetriever
+    {
+        Task<IEnumerable<OutlookTask>> ListAsync();
+    }
+}

src/Todo.Core/Todo.Core.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Graph.Auth" Version="1.0.0-preview.1" />
+    <PackageReference Include="Microsoft.Graph.Beta" Version="0.8.0-preview" />
+  </ItemGroup>
+
+</Project>

src/Todo.Core/TodoItemRetriever.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.Graph;
+
+namespace Todo.Core
+{
+    public class TodoItemRetriever : ITodoItemRetriever
+    {
+        private IAuthenticationProvider AuthenticationProvider { get; }
+
+        public TodoItemRetriever(IAuthenticationProvider authenticationProvider)
+        {
+            AuthenticationProvider = authenticationProvider;
+        }
+
+        public async Task<IEnumerable<OutlookTask>> ListAsync()
+        {
+            var graphServiceClient = new GraphServiceClient(AuthenticationProvider);
+            return await graphServiceClient.Me.Outlook.Tasks.Request().GetAsync();
+        }
+    }
+}