Initial commit.

OnPremiseApp/App.xaml

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+<Application x:Class="ClientApiPoC.OnPremiseApp.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:ClientApiPoC.OnPremiseApp">
+    <Application.Resources>
+         
+    </Application.Resources>
+</Application>

OnPremiseApp/App.xaml.cs

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+using System.Windows;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using ClientApiPoC.OnPremiseApp.Services;
+
+namespace ClientApiPoC.OnPremiseApp {
+    public partial class App : Application {
+        private IHost _host;
+
+        public App() {
+            _host = Host.CreateDefaultBuilder().ConfigureServices(services => {
+                // Services:
+                services.AddSingleton<ClientDataService>();
+                // ViewModels:
+                services.AddTransient<MainWindowViewModel>();
+                // Views:
+                services.AddSingleton<MainWindow>();
+            }).Build();
+        }
+
+        protected override async void OnStartup(StartupEventArgs e) {
+            await _host.StartAsync();
+
+            var window = _host.Services.GetRequiredService<MainWindow>();
+            window.Show();
+
+            base.OnStartup(e);
+        }
+
+        protected override async void OnExit(ExitEventArgs e) {
+            await _host.StopAsync();
+            _host.Dispose();
+            base.OnExit(e);
+        }
+    }
+}

OnPremiseApp/AssemblyInfo.cs

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+using System.Windows;
+
+[assembly: ThemeInfo(
+    ResourceDictionaryLocation.None,            //where theme specific resource dictionaries are located
+                                                //(used if a resource is not found in the page,
+                                                // or application resource dictionaries)
+    ResourceDictionaryLocation.SourceAssembly   //where the generic resource dictionary is located
+                                                //(used if a resource is not found in the page,
+                                                // app, or any theme specific resource dictionaries)
+)]

OnPremiseApp/MainWindow.xaml

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+<wpf:MvvmWindow x:TypeArguments="local:MainWindowViewModel"
+                x:Class="ClientApiPoC.OnPremiseApp.MainWindow"
+                xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+                xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+                xmlns:local="clr-namespace:ClientApiPoC.OnPremiseApp"
+                xmlns:wpf="clr-namespace:ClientApiPoC.Shared.Wpf;assembly=Shared.Wpf"
+                xmlns:b="http://schemas.microsoft.com/xaml/behaviors"
+                mc:Ignorable="d"
+                Title="On-Premise Gateway"
+                Width="384"
+                Height="AUTO"
+                MaxHeight="144"
+                ResizeMode="CanMinimize"
+                WindowStartupLocation="CenterScreen">
+    <Grid RowDefinitions="AUTO, AUTO"
+          ColumnDefinitions="*, AUTO"
+          Margin="12">
+
+        <Grid Grid.Row="0"
+              Grid.Column="0"
+              RowDefinitions="AUTO, AUTO"
+              ColumnDefinitions="*">
+
+            <TextBlock Grid.Row="0"
+                       Grid.Column="0"
+                       Text="Base-URL:" />
+
+            <TextBox Grid.Row="1"
+                     Grid.Column="0"
+                     VerticalAlignment="Center"
+                     IsEnabled="{Binding UrlTextFieldEnabled}"
+                     Text="{Binding ApiServiceUrl}" />
+
+        </Grid>
+
+        <Button Grid.Row="0"
+                Grid.Column="1"
+                VerticalAlignment="Stretch"
+                Padding="5"
+                Margin="5, 0, 0, 0"
+                Content="{Binding ConnectButtonText}"
+                IsEnabled="{Binding ConnectButtonEnabled}"
+                Command="{Binding ToggleConnectionCommand}" />
+
+        <Grid Grid.Row="1"
+              Grid.Column="0"
+              RowDefinitions="AUTO, AUTO"
+              ColumnDefinitions="*"
+              Margin="0, 12, 0, 0">
+
+            <TextBlock Grid.Row="0"
+                       Grid.Column="0"
+                       Text="Local client data:" />
+
+            <TextBox Grid.Row="1"
+                     Grid.Column="0"
+                     VerticalAlignment="Center"
+                     Text="{Binding LocalClientData, UpdateSourceTrigger=PropertyChanged}">
+            </TextBox>
+
+        </Grid>
+
+        <Button Grid.Row="1"
+                Grid.Column="1"
+                VerticalAlignment="Stretch"
+                Padding="5"
+                Margin="5, 12, 0, 0"
+                IsDefault="True"
+                Content="Set data"
+                IsEnabled="{Binding SetLocalClientDataButtonEnabled}"
+                Command="{Binding SetLocalClientDataCommand}" />
+
+    </Grid>
+</wpf:MvvmWindow>

OnPremiseApp/MainWindow.xaml.cs

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+using ClientApiPoC.Shared.Wpf;
+
+namespace ClientApiPoC.OnPremiseApp {
+    public partial class MainWindow : MvvmWindow<MainWindowViewModel> {
+        public MainWindow(MainWindowViewModel viewModel) : base(viewModel) {
+            InitializeComponent();
+        }
+    }
+}

OnPremiseApp/MainWindowViewModel.cs

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+using System.ComponentModel;
+using System.Windows.Input;
+using CommunityToolkit.Mvvm.Input;
+using ClientApiPoC.OnPremiseApp.Services;
+using ClientApiPoC.Shared;
+using ClientApiPoC.Shared.Wpf;
+using ClientApiPoC.Shared.SignalR;
+
+namespace ClientApiPoC.OnPremiseApp {
+    public class MainWindowViewModel : BaseViewModel {
+        private ClientDataService _clientDataService;
+        private TunnelClient _tunnelClient;
+
+        #region Properties
+        private string _apiServiceUrl = "http://localhost:5228/";
+        public string ApiServiceUrl {
+            get => _apiServiceUrl;
+            set {
+                _apiServiceUrl = value;
+                OnPropertyChanged(nameof(ApiServiceUrl));
+            }
+        }
+
+        private bool _tunnelClientIsConnecting = false;
+        public bool TunnelClientIsConnecting {
+            get => _tunnelClientIsConnecting;
+            set {
+                _tunnelClientIsConnecting = value;
+                OnPropertyChanged(nameof(TunnelClientIsConnecting));
+                OnPropertyChanged(nameof(ConnectButtonEnabled));
+                OnPropertyChanged(nameof(UrlTextFieldEnabled));
+            }
+        }
+
+        public bool TunnelClientConnected => (_tunnelClient.IsConnected || _tunnelClient.IsConnecting);
+
+        public string ConnectButtonText => (this.TunnelClientConnected ? "Disconnect" : "Connect");
+
+        public bool ConnectButtonEnabled => !this.TunnelClientIsConnecting;
+
+        public bool UrlTextFieldEnabled => !this.TunnelClientIsConnecting && !this.TunnelClientConnected;
+
+        private string _localClientData = "";
+        public string LocalClientData {
+            get => _localClientData;
+            set {
+                _localClientData = value;
+                OnPropertyChanged(nameof(LocalClientData));
+                OnPropertyChanged(nameof(SetLocalClientDataButtonEnabled));
+            }
+        }
+
+        public bool SetLocalClientDataButtonEnabled {
+            get {
+                if (string.IsNullOrEmpty(this.LocalClientData) && string.IsNullOrEmpty(_clientDataService.ClientData)) return false;
+                return !string.Equals(this.LocalClientData, _clientDataService.ClientData);
+            }
+        }
+        #endregion
+
+        #region Commands
+        public ICommand ToggleConnectionCommand { get; }
+
+        public ICommand SetLocalClientDataCommand { get; }
+        #endregion
+
+        public MainWindowViewModel(ClientDataService clientDataService) {
+            if (clientDataService == null) throw new ArgumentNullException(nameof(clientDataService));
+            _clientDataService = clientDataService;
+            _tunnelClient = new TunnelClient();
+            _tunnelClient.PropertyChanged += TunnelClient_PropertyChanged;
+            this.ToggleConnectionCommand = new AsyncRelayCommand(ToggleConnectionAsync);
+            this.SetLocalClientDataCommand = new AsyncRelayCommand(SetLocalClientDataAsync);
+        }
+
+        private void TunnelClient_PropertyChanged(object? sender, PropertyChangedEventArgs e) {
+            OnPropertyChanged(nameof(TunnelClientConnected));
+            OnPropertyChanged(nameof(ConnectButtonText));
+            OnPropertyChanged(nameof(UrlTextFieldEnabled));
+        }
+
+        private async Task ToggleConnectionAsync() {
+            if (this.TunnelClientIsConnecting) return;
+            try {
+                this.TunnelClientIsConnecting = true;
+                if (this.TunnelClientConnected) {
+                    await _tunnelClient.DisconnectAsync();
+                } else {
+                    var url = this.ApiServiceUrl;
+                    if (string.IsNullOrWhiteSpace(url)) throw new Exception("Please provide a base url.");
+                    while (url.EndsWith('/')) url = url[..^1];
+                    url += Routes.TUNNEL_PATH;
+                    await _tunnelClient.ConnectAsync(url, _clientDataService.ConfigureTunnelActions);
+                }
+            } catch (Exception ex) {
+                await HandleErrorAsync(ex);
+            } finally {
+                this.TunnelClientIsConnecting = false;
+            }
+        }
+
+        private async Task SetLocalClientDataAsync() {
+            try {
+                string? newClientData = this.LocalClientData;
+                if (string.IsNullOrEmpty(newClientData)) newClientData = null;
+                _clientDataService.ClientData = newClientData;
+            } catch (Exception ex) {
+                await HandleErrorAsync(ex);
+            } finally {
+                OnPropertyChanged(nameof(SetLocalClientDataButtonEnabled));
+            }
+        }
+    }
+}

OnPremiseApp/OnPremiseApp.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <UseWPF>true</UseWPF>
+    
+    <RootNamespace>ClientApiPoC.OnPremiseApp</RootNamespace>
+
+    <PublishSingleFile>true</PublishSingleFile>
+    <SelfContained>true</SelfContained>
+    <IncludeNativeLibrariesForSelfExtract>true</IncludeNativeLibrariesForSelfExtract>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+    <EnableCompressionInSingleFile>true</EnableCompressionInSingleFile>
+    <PublishTrimmed>false</PublishTrimmed>
+
+    <Company>Mike Schumann</Company>
+    <Copyright>Copyright © 2026 $(Company)</Copyright>
+    <AssemblyVersion>0.1.0</AssemblyVersion>
+    <FileVersion>$(AssemblyVersion)</FileVersion>
+    <NeutralLanguage>en-US</NeutralLanguage>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
+    <DebugType>portable</DebugType>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Release'">
+    <DebugType>none</DebugType>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="10.0.5" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.5" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Shared.Wpf\Shared.Wpf.csproj" />
+    <ProjectReference Include="..\Shared\Shared.csproj" />
+  </ItemGroup>
+
+</Project>

OnPremiseApp/Properties/PublishProfiles/FolderProfile.pubxml

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+<?xml version="1.0" encoding="utf-8"?>
+<!-- https://go.microsoft.com/fwlink/?LinkID=208121. -->
+<Project>
+  <PropertyGroup>
+    <Configuration>Release</Configuration>
+    <Platform>Any CPU</Platform>
+    <PublishDir>..\Publish\</PublishDir>
+    <PublishProtocol>FileSystem</PublishProtocol>
+    <_TargetId>Folder</_TargetId>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+    <SelfContained>true</SelfContained>
+    <PublishReadyToRun>false</PublishReadyToRun>
+  </PropertyGroup>
+</Project>

OnPremiseApp/Services/ClientDataService.cs

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+using Microsoft.AspNetCore.SignalR.Client;
+using ClientApiPoC.Shared.Models;
+
+namespace ClientApiPoC.OnPremiseApp.Services {
+    public class ClientDataService {
+        public string? ClientData { get; set; } = null;
+
+        public async Task<ClientDataModel> GetClientDataAsync(DateTime timestampServer) {
+            return new ClientDataModel() {
+                Data = this.ClientData,
+                TimestampServerUtc = timestampServer,
+                TimestampClientUtc = DateTime.UtcNow
+            };
+        }
+
+        public void ConfigureTunnelActions(HubConnection tunnelConnection) {
+            if (tunnelConnection == null) throw new ArgumentNullException(nameof(tunnelConnection));
+            tunnelConnection.On<DateTime, ClientDataModel>("GetClientData", GetClientDataAsync);
+        }
+    }
+}