From 39c8b861c0de844ab24b8b56431f60fdbc0d50c3 Mon Sep 17 00:00:00 2001
From: Mike Schumann <Mike@DieSchumanns.net>
Date: Fri, 13 Mar 2026 10:23:47 +0100
Subject: [PATCH] Initial commit.

---
 .gitignore                                    |   6 +-
 ApiClient/ApiClient.csproj                    |  45 +++++++
 ApiClient/App.xaml                            |   8 ++
 ApiClient/App.xaml.cs                         |  33 +++++
 ApiClient/AssemblyInfo.cs                     |  10 ++
 ApiClient/MainWindow.xaml                     |  62 ++++++++++
 ApiClient/MainWindow.xaml.cs                  |  10 ++
 ApiClient/MainWindowViewModel.cs              |  92 ++++++++++++++
 .../PublishProfiles/FolderProfile.pubxml      |  15 +++
 ApiService/ApiService.csproj                  |  41 +++++++
 .../Controllers/ExampleRequestController.cs   |  27 +++++
 ApiService/Program.cs                         |  34 ++++++
 .../PublishProfiles/FolderProfile.pubxml      |  20 +++
 ApiService/Properties/launchSettings.json     |  14 +++
 ApiService/TunnelServer.cs                    |  24 ++++
 ApiService/appsettings.Development.json       |   8 ++
 ApiService/appsettings.json                   |  16 +++
 ApiService/dotnet-tools.json                  |  13 ++
 ClientApiPoC.slnx                             |   7 ++
 OnPremiseApp/App.xaml                         |   8 ++
 OnPremiseApp/App.xaml.cs                      |  36 ++++++
 OnPremiseApp/AssemblyInfo.cs                  |  10 ++
 OnPremiseApp/MainWindow.xaml                  |  76 ++++++++++++
 OnPremiseApp/MainWindow.xaml.cs               |   9 ++
 OnPremiseApp/MainWindowViewModel.cs           | 114 ++++++++++++++++++
 OnPremiseApp/OnPremiseApp.csproj              |  45 +++++++
 .../PublishProfiles/FolderProfile.pubxml      |  15 +++
 OnPremiseApp/Services/ClientDataService.cs    |  21 ++++
 README.md                                     |  21 +++-
 Shared.Wpf/BaseViewModel.cs                   |  11 ++
 Shared.Wpf/MvvmWindow.cs                      |  13 ++
 Shared.Wpf/Shared.Wpf.csproj                  |  23 ++++
 Shared/Models/ClientDataModel.cs              |   9 ++
 Shared/Models/ClientResultModel.cs            |   7 ++
 Shared/Models/ExampleRequestResultModel.cs    |   7 ++
 Shared/NotifyPropertyChangedBase.cs           |  12 ++
 Shared/Routes.cs                              |   9 ++
 Shared/Shared.csproj                          |  23 ++++
 Shared/SignalR/ClientTracker.cs               |  18 +++
 Shared/SignalR/TunnelClient.cs                |  84 +++++++++++++
 Shared/SignalR/TunnelHub.cs                   |  20 +++
 Shared/SignalR/TunnelHubExtensions.cs         |  21 ++++
 Shared/SignalR/TunnelServerBase.cs            |  36 ++++++
 Shared/Tools.cs                               |  15 +++
 44 files changed, 1144 insertions(+), 4 deletions(-)
 create mode 100644 ApiClient/ApiClient.csproj
 create mode 100644 ApiClient/App.xaml
 create mode 100644 ApiClient/App.xaml.cs
 create mode 100644 ApiClient/AssemblyInfo.cs
 create mode 100644 ApiClient/MainWindow.xaml
 create mode 100644 ApiClient/MainWindow.xaml.cs
 create mode 100644 ApiClient/MainWindowViewModel.cs
 create mode 100644 ApiClient/Properties/PublishProfiles/FolderProfile.pubxml
 create mode 100644 ApiService/ApiService.csproj
 create mode 100644 ApiService/Controllers/ExampleRequestController.cs
 create mode 100644 ApiService/Program.cs
 create mode 100644 ApiService/Properties/PublishProfiles/FolderProfile.pubxml
 create mode 100644 ApiService/Properties/launchSettings.json
 create mode 100644 ApiService/TunnelServer.cs
 create mode 100644 ApiService/appsettings.Development.json
 create mode 100644 ApiService/appsettings.json
 create mode 100644 ApiService/dotnet-tools.json
 create mode 100644 ClientApiPoC.slnx
 create mode 100644 OnPremiseApp/App.xaml
 create mode 100644 OnPremiseApp/App.xaml.cs
 create mode 100644 OnPremiseApp/AssemblyInfo.cs
 create mode 100644 OnPremiseApp/MainWindow.xaml
 create mode 100644 OnPremiseApp/MainWindow.xaml.cs
 create mode 100644 OnPremiseApp/MainWindowViewModel.cs
 create mode 100644 OnPremiseApp/OnPremiseApp.csproj
 create mode 100644 OnPremiseApp/Properties/PublishProfiles/FolderProfile.pubxml
 create mode 100644 OnPremiseApp/Services/ClientDataService.cs
 create mode 100644 Shared.Wpf/BaseViewModel.cs
 create mode 100644 Shared.Wpf/MvvmWindow.cs
 create mode 100644 Shared.Wpf/Shared.Wpf.csproj
 create mode 100644 Shared/Models/ClientDataModel.cs
 create mode 100644 Shared/Models/ClientResultModel.cs
 create mode 100644 Shared/Models/ExampleRequestResultModel.cs
 create mode 100644 Shared/NotifyPropertyChangedBase.cs
 create mode 100644 Shared/Routes.cs
 create mode 100644 Shared/Shared.csproj
 create mode 100644 Shared/SignalR/ClientTracker.cs
 create mode 100644 Shared/SignalR/TunnelClient.cs
 create mode 100644 Shared/SignalR/TunnelHub.cs
 create mode 100644 Shared/SignalR/TunnelHubExtensions.cs
 create mode 100644 Shared/SignalR/TunnelServerBase.cs
 create mode 100644 Shared/Tools.cs

diff --git a/.gitignore b/.gitignore
index ed6d1d2..b491d6a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -180,15 +180,15 @@ DocProject/Help/Html2
 DocProject/Help/html
 
 # Click-Once directory
-publish/
+[Pp]ublish/
 
 # Publish Web Output
 *.[Pp]ublish.xml
 *.azurePubxml
 # Note: Comment the next line if you want to checkin your web deploy settings,
 # but database connection strings (with potential passwords) will be unencrypted
-*.pubxml
-*.publishproj
+#*.pubxml
+#*.publishproj
 
 # Microsoft Azure Web App publish settings. Comment the next line if you want to
 # checkin your Azure Web App publish settings, but sensitive information contained
diff --git a/ApiClient/ApiClient.csproj b/ApiClient/ApiClient.csproj
new file mode 100644
index 0000000..6cc66f4
--- /dev/null
+++ b/ApiClient/ApiClient.csproj
@@ -0,0 +1,45 @@
+<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.ApiClient</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>
diff --git a/ApiClient/App.xaml b/ApiClient/App.xaml
new file mode 100644
index 0000000..2059c88
--- /dev/null
+++ b/ApiClient/App.xaml
@@ -0,0 +1,8 @@
+<Application x:Class="ClientApiPoC.ApiClient.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:ClientApiPoC.ApiClient">
+    <Application.Resources>
+         
+    </Application.Resources>
+</Application>
diff --git a/ApiClient/App.xaml.cs b/ApiClient/App.xaml.cs
new file mode 100644
index 0000000..b003b04
--- /dev/null
+++ b/ApiClient/App.xaml.cs
@@ -0,0 +1,33 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using System.Windows;
+
+namespace ClientApiPoC.ApiClient {
+    public partial class App : Application {
+        private IHost _host;
+
+        public App() {
+            _host = Host.CreateDefaultBuilder().ConfigureServices(services => {
+                // 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);
+        }
+    }
+}
\ No newline at end of file
diff --git a/ApiClient/AssemblyInfo.cs b/ApiClient/AssemblyInfo.cs
new file mode 100644
index 0000000..b0ec827
--- /dev/null
+++ b/ApiClient/AssemblyInfo.cs
@@ -0,0 +1,10 @@
+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)
+)]
diff --git a/ApiClient/MainWindow.xaml b/ApiClient/MainWindow.xaml
new file mode 100644
index 0000000..12fdf09
--- /dev/null
+++ b/ApiClient/MainWindow.xaml
@@ -0,0 +1,62 @@
+<wpf:MvvmWindow x:TypeArguments="local:MainWindowViewModel"
+                x:Class="ClientApiPoC.ApiClient.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.ApiClient"
+                xmlns:wpf="clr-namespace:ClientApiPoC.Shared.Wpf;assembly=Shared.Wpf"
+                mc:Ignorable="d"
+                Title="API-Client"
+                Width="512"
+                Height="384"
+                ResizeMode="CanMinimize">
+    <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 ControlsEnabled}"
+                     Text="{Binding ApiServiceUrl}" />
+
+        </Grid>
+
+        <Button Grid.Row="0"
+                Grid.Column="1"
+                VerticalAlignment="Stretch"
+                Padding="5"
+                Margin="5, 0, 0, 0"
+                IsDefault="True"
+                Content="HTTP-GET"
+                IsEnabled="{Binding ControlsEnabled}"
+                Command="{Binding HttpGetButtonCommand}" />
+
+        <TextBlock Grid.Row="1"
+                   Grid.Column="0"
+                   Grid.ColumnSpan="2"
+                   Margin="0, 5, 0, 0"
+                   Text="Result:" />
+
+        <TextBox Grid.Row="2"
+                 Grid.Column="0"
+                 Grid.ColumnSpan="2"
+                 Padding="5"
+                 HorizontalScrollBarVisibility="Auto"
+                 VerticalScrollBarVisibility="Auto"
+                 IsReadOnly="True"
+                 FontFamily="Consolas"
+                 Text="{Binding RequestResultDataString, Mode=OneWay}" />
+
+    </Grid>
+</wpf:MvvmWindow>
\ No newline at end of file
diff --git a/ApiClient/MainWindow.xaml.cs b/ApiClient/MainWindow.xaml.cs
new file mode 100644
index 0000000..6720d26
--- /dev/null
+++ b/ApiClient/MainWindow.xaml.cs
@@ -0,0 +1,10 @@
+using ClientApiPoC.Shared.Wpf;
+using System.Windows;
+
+namespace ClientApiPoC.ApiClient {
+    public partial class MainWindow : MvvmWindow<MainWindowViewModel> {
+        public MainWindow(MainWindowViewModel viewModel) : base(viewModel) {
+            InitializeComponent();
+        }
+    }
+}
\ No newline at end of file
diff --git a/ApiClient/MainWindowViewModel.cs b/ApiClient/MainWindowViewModel.cs
new file mode 100644
index 0000000..ca20ade
--- /dev/null
+++ b/ApiClient/MainWindowViewModel.cs
@@ -0,0 +1,92 @@
+using ClientApiPoC.Shared;
+using ClientApiPoC.Shared.Models;
+using ClientApiPoC.Shared.Wpf;
+using CommunityToolkit.Mvvm.Input;
+using System.Net.Http;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Windows.Input;
+
+namespace ClientApiPoC.ApiClient {
+    public class MainWindowViewModel : BaseViewModel {
+        #region Properties
+        private string _apiServiceUrl = "http://localhost:5228/";
+        public string ApiServiceUrl {
+            get => _apiServiceUrl;
+            set {
+                _apiServiceUrl = value;
+                OnPropertyChanged(nameof(ApiServiceUrl));
+            }
+        }
+
+        private bool _isFetchingData = false;
+        public bool IsFetchingData {
+            get => _isFetchingData;
+            set {
+                _isFetchingData = value;
+                OnPropertyChanged(nameof(IsFetchingData));
+                OnPropertyChanged(nameof(ControlsEnabled));
+            }
+        }
+
+        public bool ControlsEnabled => !this.IsFetchingData;
+
+        private ExampleRequestResultModel? _requestResultData = null;
+        public ExampleRequestResultModel? RequestResultData {
+            get => _requestResultData;
+            set {
+                _requestResultData = value;
+                OnPropertyChanged(nameof(RequestResultData));
+                OnPropertyChanged(nameof(RequestResultDataString));
+            }
+        }
+
+        public string RequestResultDataString {
+            get {
+                if (this.RequestResultData == null) return "NULL";
+                var options = new JsonSerializerOptions() {
+                    IndentCharacter = ' ',
+                    IndentSize = 2,
+                    NewLine = "\n",
+                    WriteIndented = true
+                };
+                return JsonSerializer.Serialize(this.RequestResultData, options);
+            }
+        }
+        #endregion
+
+        #region Commands
+        public ICommand HttpGetButtonCommand { get; }
+        #endregion
+
+        public MainWindowViewModel() {
+            this.HttpGetButtonCommand = new AsyncRelayCommand(HttpGetButtonActionAsync);
+        }
+
+        private async Task HttpGetButtonActionAsync() {
+            if (this.IsFetchingData) return;
+            try {
+                this.IsFetchingData = true;
+                var url = this.ApiServiceUrl;
+                if (string.IsNullOrWhiteSpace(url)) throw new InvalidOperationException("No base url specified.");
+                while (url.EndsWith('/')) url = url[..^1];
+                url += Routes.EXAMPLE_REQUEST;
+                using (var httpClient = Tools.CreateHttpClient()) {
+                    var request = new HttpRequestMessage(HttpMethod.Get, url);
+                    var response = await httpClient.SendAsync(request);
+                    response.EnsureSuccessStatusCode();
+                    var responseString = await response.Content.ReadAsStringAsync();
+                    var options = new JsonSerializerOptions() {
+                        PropertyNameCaseInsensitive = true
+                    };
+                    var result = JsonSerializer.Deserialize<ExampleRequestResultModel>(responseString, options);
+                    this.RequestResultData = result;
+                }
+            } catch (Exception ex) {
+                await HandleErrorAsync(ex);
+            } finally {
+                this.IsFetchingData = false;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/ApiClient/Properties/PublishProfiles/FolderProfile.pubxml b/ApiClient/Properties/PublishProfiles/FolderProfile.pubxml
new file mode 100644
index 0000000..365cb40
--- /dev/null
+++ b/ApiClient/Properties/PublishProfiles/FolderProfile.pubxml
@@ -0,0 +1,15 @@
+<?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>
\ No newline at end of file
diff --git a/ApiService/ApiService.csproj b/ApiService/ApiService.csproj
new file mode 100644
index 0000000..6a3a16c
--- /dev/null
+++ b/ApiService/ApiService.csproj
@@ -0,0 +1,41 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    
+    <RootNamespace>ClientApiPoC.ApiService</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="Microsoft.AspNetCore.OpenApi" Version="10.0.5" />
+    <PackageReference Include="Swashbuckle.AspNetCore.SwaggerUI" Version="10.1.5" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Shared\Shared.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/ApiService/Controllers/ExampleRequestController.cs b/ApiService/Controllers/ExampleRequestController.cs
new file mode 100644
index 0000000..3d5f9cc
--- /dev/null
+++ b/ApiService/Controllers/ExampleRequestController.cs
@@ -0,0 +1,27 @@
+using ClientApiPoC.Shared;
+using ClientApiPoC.Shared.Models;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ClientApiPoC.ApiService.Controllers {
+    [ApiController]
+    [Route(Routes.EXAMPLE_REQUEST)]
+    public class ExampleRequestController : ControllerBase {
+        private readonly TunnelServer _tunnel;
+
+        public ExampleRequestController(TunnelServer tunnel) {
+            if (tunnel == null) throw new ArgumentNullException(nameof(tunnel));
+            _tunnel = tunnel;
+        }
+
+        [HttpGet]
+        public async Task<ExampleRequestResultModel> Get() {
+            // Daten der Clients abfragen...
+            var clients = await _tunnel.GetDataFromAllClientsAsync();
+            var result = new ExampleRequestResultModel() {
+                ServerMessage = "Hello, world!",
+                Clients = clients
+            };
+            return result;
+        }
+    }
+}
\ No newline at end of file
diff --git a/ApiService/Program.cs b/ApiService/Program.cs
new file mode 100644
index 0000000..0704b67
--- /dev/null
+++ b/ApiService/Program.cs
@@ -0,0 +1,34 @@
+using ClientApiPoC.Shared;
+using ClientApiPoC.Shared.SignalR;
+
+namespace ClientApiPoC.ApiService {
+    public class Program {
+        public static void Main(string[] args) {
+            var builder = WebApplication.CreateBuilder(args);
+
+            builder.Services.AddControllers();
+            builder.Services.AddOpenApi();
+
+            builder.Services.AddTunnelHub();
+            builder.Services.AddTransient<TunnelServer>();
+
+            var app = builder.Build();
+
+            // Configure the HTTP request pipeline.
+            if (app.Environment.IsDevelopment()) {
+                app.MapOpenApi();
+                app.UseSwaggerUI(options => {
+                    options.SwaggerEndpoint("/openapi/v1.json", "ClientApiPoC");
+                });
+            }
+
+            app.UseAuthorization();
+
+            app.MapControllers();
+
+            app.MapTunnelHub(Routes.TUNNEL_PATH);
+
+            app.Run();
+        }
+    }
+}
\ No newline at end of file
diff --git a/ApiService/Properties/PublishProfiles/FolderProfile.pubxml b/ApiService/Properties/PublishProfiles/FolderProfile.pubxml
new file mode 100644
index 0000000..1f38def
--- /dev/null
+++ b/ApiService/Properties/PublishProfiles/FolderProfile.pubxml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- https://go.microsoft.com/fwlink/?LinkID=208121. -->
+<Project>
+  <PropertyGroup>
+    <DeleteExistingFiles>true</DeleteExistingFiles>
+    <ExcludeApp_Data>false</ExcludeApp_Data>
+    <LaunchSiteAfterPublish>true</LaunchSiteAfterPublish>
+    <LastUsedBuildConfiguration>Release</LastUsedBuildConfiguration>
+    <LastUsedPlatform>Any CPU</LastUsedPlatform>
+    <PublishProvider>FileSystem</PublishProvider>
+    <PublishUrl>..\Publish\ApiService\</PublishUrl>
+    <WebPublishMethod>FileSystem</WebPublishMethod>
+    <_TargetId>Folder</_TargetId>
+    <SiteUrlToLaunchAfterPublish />
+    <TargetFramework>net10.0</TargetFramework>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+    <ProjectGuid>bb6e670a-3d3d-430e-4dd4-25ad2c7d9c26</ProjectGuid>
+    <SelfContained>true</SelfContained>
+  </PropertyGroup>
+</Project>
\ No newline at end of file
diff --git a/ApiService/Properties/launchSettings.json b/ApiService/Properties/launchSettings.json
new file mode 100644
index 0000000..a4a08e9
--- /dev/null
+++ b/ApiService/Properties/launchSettings.json
@@ -0,0 +1,14 @@
+{
+  "profiles": {
+    "http": {
+      "commandName": "Project",
+      "launchUrl": "swagger",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      },
+      "dotnetRunMessages": true,
+      "applicationUrl": "http://*:5228"
+    }
+  },
+  "$schema": "https://json.schemastore.org/launchsettings.json"
+}
\ No newline at end of file
diff --git a/ApiService/TunnelServer.cs b/ApiService/TunnelServer.cs
new file mode 100644
index 0000000..f0dc833
--- /dev/null
+++ b/ApiService/TunnelServer.cs
@@ -0,0 +1,24 @@
+using Microsoft.AspNetCore.SignalR;
+using ClientApiPoC.Shared.SignalR;
+using ClientApiPoC.Shared.Models;
+
+namespace ClientApiPoC.ApiService {
+    public class TunnelServer : TunnelServerBase {
+        public TunnelServer(IHubContext<TunnelHub> hubContext, ClientTracker clientTracker) : base(hubContext, clientTracker) { }
+
+        public async Task<IEnumerable<ClientResultModel>> GetDataFromAllClientsAsync() {
+            var timestampServer = DateTime.UtcNow;
+            var results = new List<ClientResultModel>();
+            var clients = this.GetAllClients();
+            foreach (var client in clients) {
+                var clientData = await client.Value.InvokeAsync<ClientDataModel>("GetClientData", timestampServer, CancellationToken.None);
+                var result = new ClientResultModel() {
+                    ClientId = client.Key,
+                    ClientData = clientData
+                };
+                results.Add(result);
+            }
+            return results;
+        }
+    }
+}
\ No newline at end of file
diff --git a/ApiService/appsettings.Development.json b/ApiService/appsettings.Development.json
new file mode 100644
index 0000000..0c208ae
--- /dev/null
+++ b/ApiService/appsettings.Development.json
@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}
diff --git a/ApiService/appsettings.json b/ApiService/appsettings.json
new file mode 100644
index 0000000..99e592b
--- /dev/null
+++ b/ApiService/appsettings.json
@@ -0,0 +1,16 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*",
+  "Kestrel": {
+    "Endpoints": {
+      "Http": {
+        "Url": "http://*:5228"
+      }
+    }
+  }
+}
diff --git a/ApiService/dotnet-tools.json b/ApiService/dotnet-tools.json
new file mode 100644
index 0000000..b6f4c2f
--- /dev/null
+++ b/ApiService/dotnet-tools.json
@@ -0,0 +1,13 @@
+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "dotnet-ef": {
+      "version": "10.0.5",
+      "commands": [
+        "dotnet-ef"
+      ],
+      "rollForward": false
+    }
+  }
+}
\ No newline at end of file
diff --git a/ClientApiPoC.slnx b/ClientApiPoC.slnx
new file mode 100644
index 0000000..20bb135
--- /dev/null
+++ b/ClientApiPoC.slnx
@@ -0,0 +1,7 @@
+<Solution>
+  <Project Path="ApiClient/ApiClient.csproj" />
+  <Project Path="ApiService/ApiService.csproj" />
+  <Project Path="OnPremiseApp/OnPremiseApp.csproj" Id="ddccc69b-ec86-473b-b34f-317e5ff1e4cf" />
+  <Project Path="Shared.Wpf/Shared.Wpf.csproj" />
+  <Project Path="Shared/Shared.csproj" />
+</Solution>
diff --git a/OnPremiseApp/App.xaml b/OnPremiseApp/App.xaml
new file mode 100644
index 0000000..4483be4
--- /dev/null
+++ b/OnPremiseApp/App.xaml
@@ -0,0 +1,8 @@
+<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>
diff --git a/OnPremiseApp/App.xaml.cs b/OnPremiseApp/App.xaml.cs
new file mode 100644
index 0000000..f0e5d72
--- /dev/null
+++ b/OnPremiseApp/App.xaml.cs
@@ -0,0 +1,36 @@
+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);
+        }
+    }
+}
\ No newline at end of file
diff --git a/OnPremiseApp/AssemblyInfo.cs b/OnPremiseApp/AssemblyInfo.cs
new file mode 100644
index 0000000..b0ec827
--- /dev/null
+++ b/OnPremiseApp/AssemblyInfo.cs
@@ -0,0 +1,10 @@
+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)
+)]
diff --git a/OnPremiseApp/MainWindow.xaml b/OnPremiseApp/MainWindow.xaml
new file mode 100644
index 0000000..6f2189d
--- /dev/null
+++ b/OnPremiseApp/MainWindow.xaml
@@ -0,0 +1,76 @@
+<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>
\ No newline at end of file
diff --git a/OnPremiseApp/MainWindow.xaml.cs b/OnPremiseApp/MainWindow.xaml.cs
new file mode 100644
index 0000000..7658c76
--- /dev/null
+++ b/OnPremiseApp/MainWindow.xaml.cs
@@ -0,0 +1,9 @@
+using ClientApiPoC.Shared.Wpf;
+
+namespace ClientApiPoC.OnPremiseApp {
+    public partial class MainWindow : MvvmWindow<MainWindowViewModel> {
+        public MainWindow(MainWindowViewModel viewModel) : base(viewModel) {
+            InitializeComponent();
+        }
+    }
+}
\ No newline at end of file
diff --git a/OnPremiseApp/MainWindowViewModel.cs b/OnPremiseApp/MainWindowViewModel.cs
new file mode 100644
index 0000000..7515fe5
--- /dev/null
+++ b/OnPremiseApp/MainWindowViewModel.cs
@@ -0,0 +1,114 @@
+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));
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/OnPremiseApp/OnPremiseApp.csproj b/OnPremiseApp/OnPremiseApp.csproj
new file mode 100644
index 0000000..fb02090
--- /dev/null
+++ b/OnPremiseApp/OnPremiseApp.csproj
@@ -0,0 +1,45 @@
+<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>
diff --git a/OnPremiseApp/Properties/PublishProfiles/FolderProfile.pubxml b/OnPremiseApp/Properties/PublishProfiles/FolderProfile.pubxml
new file mode 100644
index 0000000..365cb40
--- /dev/null
+++ b/OnPremiseApp/Properties/PublishProfiles/FolderProfile.pubxml
@@ -0,0 +1,15 @@
+<?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>
\ No newline at end of file
diff --git a/OnPremiseApp/Services/ClientDataService.cs b/OnPremiseApp/Services/ClientDataService.cs
new file mode 100644
index 0000000..d458383
--- /dev/null
+++ b/OnPremiseApp/Services/ClientDataService.cs
@@ -0,0 +1,21 @@
+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);
+        }
+    }
+}
\ No newline at end of file
diff --git a/README.md b/README.md
index a742386..ba131de 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,21 @@
-# ClientApiPoC
+# ClientApiPoC
 
+Proof-of-Concept for transferring local data from a client to a public web service without port-forwarding, using SignalR.
+
+## ApiService
+
+Web service, serving HTTP-API for Clients (*ApiClient*). It also serves a SignalR server that local clients (*OnPremiseApp*) can connect to.
+
+This service can call a function on all connected local clients (*OnPremiseApp*) to receive local data. The local client doesn't have any HTTP-API or what so ever, nor is port-forwarding needed.
+
+API clients (*ApiClient*) can receive data from all connected local clients (*OnPremiseApp*) using the standard HTTP-API.
+
+## ApiClient
+
+This application only connects to the public HTTP-API (*ApiService*) to receive data from local clients (*OnPremiseApp*) and shows the request result.
+
+## OnPremiseApp
+
+This application connects to the *ApiService* via SignalR and transfers local data via the SignalR tunnel when the API service requests this.
+
+No Data ist actively sent to the service; the service requests data if needed.
diff --git a/Shared.Wpf/BaseViewModel.cs b/Shared.Wpf/BaseViewModel.cs
new file mode 100644
index 0000000..977fc0a
--- /dev/null
+++ b/Shared.Wpf/BaseViewModel.cs
@@ -0,0 +1,11 @@
+using System.Windows;
+
+namespace ClientApiPoC.Shared.Wpf {
+    public abstract class BaseViewModel : NotifyPropertyChangedBase {
+        protected async Task HandleErrorAsync(Exception ex) {
+            if (ex == null) return;
+            MessageBox.Show(ex.Message, "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);
+            await Task.CompletedTask;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared.Wpf/MvvmWindow.cs b/Shared.Wpf/MvvmWindow.cs
new file mode 100644
index 0000000..fee09b1
--- /dev/null
+++ b/Shared.Wpf/MvvmWindow.cs
@@ -0,0 +1,13 @@
+using System.Windows;
+
+namespace ClientApiPoC.Shared.Wpf {
+    public abstract class MvvmWindow<TViewModel> : Window where TViewModel : BaseViewModel {
+        protected TViewModel ViewModel { get; }
+
+        public MvvmWindow(TViewModel viewModel) : base() {
+            if (viewModel == null) throw new ArgumentNullException(nameof(viewModel));
+            this.ViewModel = viewModel;
+            this.DataContext = this.ViewModel;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared.Wpf/Shared.Wpf.csproj b/Shared.Wpf/Shared.Wpf.csproj
new file mode 100644
index 0000000..804d4c0
--- /dev/null
+++ b/Shared.Wpf/Shared.Wpf.csproj
@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <UseWPF>true</UseWPF>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <RootNamespace>ClientApiPoC.Shared.Wpf</RootNamespace>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
+    <DebugType>portable</DebugType>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Release'">
+    <DebugType>none</DebugType>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <ProjectReference Include="..\Shared\Shared.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/Shared/Models/ClientDataModel.cs b/Shared/Models/ClientDataModel.cs
new file mode 100644
index 0000000..8db4eac
--- /dev/null
+++ b/Shared/Models/ClientDataModel.cs
@@ -0,0 +1,9 @@
+namespace ClientApiPoC.Shared.Models {
+    public class ClientDataModel {
+        public string? Data { get; set; } = null;
+
+        public DateTime TimestampClientUtc { get; set; } = DateTime.UtcNow;
+
+        public DateTime TimestampServerUtc { get; set; } = DateTime.MinValue;
+    }
+}
\ No newline at end of file
diff --git a/Shared/Models/ClientResultModel.cs b/Shared/Models/ClientResultModel.cs
new file mode 100644
index 0000000..50cae89
--- /dev/null
+++ b/Shared/Models/ClientResultModel.cs
@@ -0,0 +1,7 @@
+namespace ClientApiPoC.Shared.Models {
+    public class ClientResultModel {
+        public string ClientId { get; set; } = "";
+
+        public ClientDataModel? ClientData { get; set; } = null;
+    }
+}
\ No newline at end of file
diff --git a/Shared/Models/ExampleRequestResultModel.cs b/Shared/Models/ExampleRequestResultModel.cs
new file mode 100644
index 0000000..e2d68eb
--- /dev/null
+++ b/Shared/Models/ExampleRequestResultModel.cs
@@ -0,0 +1,7 @@
+namespace ClientApiPoC.Shared.Models {
+    public class ExampleRequestResultModel {
+        public string? ServerMessage { get; set; }
+
+        public IEnumerable<ClientResultModel> Clients { get; set; } = [];
+    }
+}
\ No newline at end of file
diff --git a/Shared/NotifyPropertyChangedBase.cs b/Shared/NotifyPropertyChangedBase.cs
new file mode 100644
index 0000000..da3a646
--- /dev/null
+++ b/Shared/NotifyPropertyChangedBase.cs
@@ -0,0 +1,12 @@
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace ClientApiPoC.Shared {
+    public abstract class NotifyPropertyChangedBase : INotifyPropertyChanged {
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        protected void OnPropertyChanged([CallerMemberName] string? propertyName = null) {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared/Routes.cs b/Shared/Routes.cs
new file mode 100644
index 0000000..dc3e588
--- /dev/null
+++ b/Shared/Routes.cs
@@ -0,0 +1,9 @@
+namespace ClientApiPoC.Shared {
+    public static class Routes {
+        private const string BASE_PATH = "/api/";
+
+        public const string TUNNEL_PATH = "/tunnel";
+
+        public const string EXAMPLE_REQUEST = $"{BASE_PATH}ExampleRequest";
+    }
+}
\ No newline at end of file
diff --git a/Shared/Shared.csproj b/Shared/Shared.csproj
new file mode 100644
index 0000000..b35a4ef
--- /dev/null
+++ b/Shared/Shared.csproj
@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <RootNamespace>ClientApiPoC.Shared</RootNamespace>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
+    <DebugType>portable</DebugType>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Release'">
+    <DebugType>none</DebugType>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <FrameworkReference Include="Microsoft.AspNetCore.App" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="10.0.5" />
+  </ItemGroup>
+
+</Project>
diff --git a/Shared/SignalR/ClientTracker.cs b/Shared/SignalR/ClientTracker.cs
new file mode 100644
index 0000000..f01916d
--- /dev/null
+++ b/Shared/SignalR/ClientTracker.cs
@@ -0,0 +1,18 @@
+using System.Collections.Concurrent;
+
+namespace ClientApiPoC.Shared.SignalR {
+    public class ClientTracker {
+        private ConcurrentDictionary<string, string> _knownClientIds = new();
+
+        public ICollection<string> CurrentClientIds => _knownClientIds.Values;
+
+        public bool TryAddClientId(string clientId) {
+            if (string.IsNullOrWhiteSpace(clientId)) throw new ArgumentNullException(nameof(clientId));
+            return _knownClientIds.TryAdd(clientId, clientId);
+        }
+
+        public bool TryRemoveClientId(string clientId) {
+            return _knownClientIds.TryRemove(clientId, out _);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared/SignalR/TunnelClient.cs b/Shared/SignalR/TunnelClient.cs
new file mode 100644
index 0000000..6be7db3
--- /dev/null
+++ b/Shared/SignalR/TunnelClient.cs
@@ -0,0 +1,84 @@
+using Microsoft.AspNetCore.SignalR.Client;
+
+namespace ClientApiPoC.Shared.SignalR {
+    public class TunnelClient : NotifyPropertyChangedBase, IDisposable, IAsyncDisposable {
+        #region IDisposable-Implementierung
+        private bool _disposed;
+
+        protected virtual void Dispose(bool disposing) {
+            if (!_disposed) {
+                if (disposing) {
+                    _ = this.DisposeAsync();
+                }
+                _disposed = true;
+            }
+        }
+
+        public void Dispose() {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        public async ValueTask DisposeAsync() {
+            await DisconnectAsync();
+        }
+        #endregion
+
+        private HubConnection? _connection = null;
+
+        public bool IsConnected => (this.ConnectionState == HubConnectionState.Connected);
+
+        public bool IsConnecting => (this.ConnectionState == HubConnectionState.Connecting || this.ConnectionState == HubConnectionState.Reconnecting);
+
+        protected HubConnectionState ConnectionState => (_connection?.State ?? HubConnectionState.Disconnected);
+
+        public async Task ConnectAsync(string url, Action<HubConnection> configureConnection) {
+            try {
+                if (string.IsNullOrWhiteSpace(url)) throw new ArgumentNullException(nameof(url));
+                if (this.IsConnected) throw new InvalidOperationException("SignalR connection is already established.");
+                _connection = new HubConnectionBuilder().WithUrl(url).WithAutomaticReconnect().Build();
+                _connection.Reconnecting += Connection_Reconnecting;
+                _connection.Reconnected += Connection_Reconnected;
+                _connection.Closed += Connection_Closed;
+                configureConnection(_connection);
+                await _connection.StartAsync();
+            } finally {
+                await UpdateStateAsync();
+            }
+        }
+
+        public async Task DisconnectAsync() {
+            try {
+                if (_connection == null) return;
+                try {
+                    if (this.IsConnected) await _connection.StopAsync();
+                } catch { }
+                _connection.Reconnecting -= Connection_Reconnecting;
+                _connection.Reconnected -= Connection_Reconnected;
+                _connection.Closed -= Connection_Closed;
+                await _connection.DisposeAsync();
+                _connection = null;
+            } finally {
+                await UpdateStateAsync();
+            }
+        }
+
+        private async Task Connection_Reconnecting(Exception? arg) {
+            await UpdateStateAsync();
+        }
+
+        private async Task Connection_Reconnected(string? arg) {
+            await UpdateStateAsync();
+        }
+
+        private async Task Connection_Closed(Exception? arg) {
+            await UpdateStateAsync();
+        }
+
+        private async Task UpdateStateAsync() {
+            OnPropertyChanged(nameof(IsConnected));
+            OnPropertyChanged(nameof(IsConnecting));
+            await Task.CompletedTask;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared/SignalR/TunnelHub.cs b/Shared/SignalR/TunnelHub.cs
new file mode 100644
index 0000000..7130aff
--- /dev/null
+++ b/Shared/SignalR/TunnelHub.cs
@@ -0,0 +1,20 @@
+using Microsoft.AspNetCore.SignalR;
+
+namespace ClientApiPoC.Shared.SignalR {
+    public sealed class TunnelHub : Hub {
+        private ClientTracker _clientTracker;
+
+        public TunnelHub(ClientTracker clientTracker) : base() {
+            if (clientTracker == null) throw new ArgumentNullException(nameof(clientTracker));
+            _clientTracker = clientTracker;
+        }
+
+        public override sealed async Task OnConnectedAsync() {
+            _ = _clientTracker.TryAddClientId(this.Context.ConnectionId);
+        }
+
+        public override sealed async Task OnDisconnectedAsync(Exception exception) {
+            _ = _clientTracker.TryRemoveClientId(this.Context.ConnectionId);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared/SignalR/TunnelHubExtensions.cs b/Shared/SignalR/TunnelHubExtensions.cs
new file mode 100644
index 0000000..36ed24e
--- /dev/null
+++ b/Shared/SignalR/TunnelHubExtensions.cs
@@ -0,0 +1,21 @@
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace ClientApiPoC.Shared.SignalR {
+    public static class TunnelHubExtensions {
+        public static IServiceCollection AddTunnelHub(this IServiceCollection services) {
+            services.AddSignalR(options => {
+                // Nachrichtengröße auf max. 16MB bringen (Standard = 32KB).
+                options.MaximumReceiveMessageSize = (16 * 1024 * 1024);
+            });
+            services.AddSingleton<ClientTracker>();
+            return services;
+        }
+
+        public static HubEndpointConventionBuilder MapTunnelHub(this IEndpointRouteBuilder app, [StringSyntax("Route")] string pattern) {
+            return app.MapHub<TunnelHub>(pattern);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared/SignalR/TunnelServerBase.cs b/Shared/SignalR/TunnelServerBase.cs
new file mode 100644
index 0000000..fc3072d
--- /dev/null
+++ b/Shared/SignalR/TunnelServerBase.cs
@@ -0,0 +1,36 @@
+using Microsoft.AspNetCore.SignalR;
+
+namespace ClientApiPoC.Shared.SignalR {
+    public abstract class TunnelServerBase {
+        protected IHubContext<TunnelHub> HubContext { get; private set; }
+
+        protected ClientTracker Clients { get; private set; }
+
+        public TunnelServerBase(IHubContext<TunnelHub> hubContext, ClientTracker clientTracker) {
+            if (hubContext == null) throw new ArgumentNullException(nameof(hubContext));
+            if (clientTracker == null) throw new ArgumentNullException(nameof(clientTracker));
+            this.HubContext = hubContext;
+            this.Clients = clientTracker;
+        }
+
+        protected ISingleClientProxy? TryGetClient(string clientId) {
+            ISingleClientProxy? client;
+            try {
+                client = this.HubContext.Clients.Client(clientId);
+            } catch {
+                client = null;
+            }
+            return client;
+        }
+
+        protected IDictionary<string, ISingleClientProxy> GetAllClients() {
+            var results = new Dictionary<string, ISingleClientProxy>();
+            var allClientIds = this.Clients.CurrentClientIds;
+            foreach (var clientId in allClientIds) {
+                var client = TryGetClient(clientId);
+                if (client != null) results.Add(clientId, client);
+            }
+            return results;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Shared/Tools.cs b/Shared/Tools.cs
new file mode 100644
index 0000000..90775e1
--- /dev/null
+++ b/Shared/Tools.cs
@@ -0,0 +1,15 @@
+using System.Net.Http;
+
+namespace ClientApiPoC.Shared {
+    public static class Tools {
+        public static HttpClient CreateHttpClient() {
+            var httpClientHandler = new HttpClientHandler() {
+                ServerCertificateCustomValidationCallback = (message, cert, chain, sslPolicyErrors) => {
+                    // HACK: Allen SSL-Zertifikaten vertrauen!
+                    return true;
+                }
+            };
+            return new HttpClient(httpClientHandler);
+        }
+    }
+}
\ No newline at end of file