Add authentication for secure document access

Introduced a new login page (`Login.razor`) to handle user authentication via access codes. Implemented `AuthService` to validate access codes through an API. Updated `ReportViewer.razor` to check user access and redirect unauthorized users to the login page. Modified `Program.cs` to register `AuthService` for dependency injection. Enhanced document fetching in `ReportViewer.razor` to ensure secure access control.

EnvelopeGenerator.ReceiverUI/Pages/Login.razor

@@ -0,0 +1,71 @@
+@page "/login/{EnvelopeKey}"
+@using EnvelopeGenerator.ReceiverUI.Options
+@using Microsoft.Extensions.Options
+
+<div class="login-page-wrapper d-flex align-items-center justify-content-center min-vh-100 bg-light">
+    <div class="card shadow-sm" style="max-width: 420px; width: 100%;">
+        <div class="card-body p-4">
+
+            <h4 class="card-title mb-1">Zugang zum Dokument</h4>
+            <p class="text-muted mb-4" style="font-size: 0.9rem;">
+                Bitte geben Sie den Zugangscode ein, den Sie per E-Mail erhalten haben, um das Dokument zu öffnen.
+            </p>
+
+            @if (!string.IsNullOrWhiteSpace(ErrorMessage)) {
+                <div class="alert alert-danger py-2">@ErrorMessage</div>
+            }
+
+            <div class="mb-3">
+                <label class="form-label" for="login-access-code">Zugangscode</label>
+                <input id="login-access-code"
+                       type="password"
+                       class="form-control"
+                       placeholder="Zugangscode eingeben"
+                       @bind="AccessCode"
+                       @bind:event="oninput"
+                       @onkeydown="OnKeyDownAsync"
+                       disabled="@IsLoading" />
+            </div>
+
+            <button class="btn btn-primary w-100"
+                    @onclick="SubmitAsync"
+                    disabled="@(IsLoading || string.IsNullOrWhiteSpace(AccessCode))">
+                @if (IsLoading) {
+                    <span class="spinner-border spinner-border-sm me-2" role="status" aria-hidden="true"></span>
+                    <span>Überprüfen …</span>
+                } else {
+                    <span>Weiter</span>
+                }
+            </button>
+
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public string EnvelopeKey { get; set; } = string.Empty;
+
+    string AccessCode = string.Empty;
+    string? ErrorMessage;
+    bool IsLoading;
+
+    async Task OnKeyDownAsync(Microsoft.AspNetCore.Components.Web.KeyboardEventArgs e) {
+        if (e.Key == "Enter")
+            await SubmitAsync();
+    }
+
+    async Task SubmitAsync() {
+        if (string.IsNullOrWhiteSpace(AccessCode)) return;
+
+        IsLoading = true;
+        ErrorMessage = null;
+        await InvokeAsync(StateHasChanged);
+
+        // TODO: API entegrasyonu buraya eklenecek
+        await Task.Delay(500); // placeholder
+
+        IsLoading = false;
+        ErrorMessage = "Der eingegebene Zugangscode ist ungültig. Bitte versuchen Sie es erneut.";
+        await InvokeAsync(StateHasChanged);
+    }
+}

EnvelopeGenerator.ReceiverUI/Pages/ReportViewer.razor

@@ -19,8 +19,10 @@
 @using EnvelopeGenerator.ReceiverUI.Options
 @inject IJSRuntime JSRuntime
 @inject IOptions<ApiOptions> AppOptions
+@inject NavigationManager Navigation
 @inject InMemoryReportStorageWebExtension ReportStorage
 @inject EnvelopeGenerator.ReceiverUI.Services.DocumentService DocumentService
+@inject EnvelopeGenerator.ReceiverUI.Services.AuthService AuthService
 
 <link href="_content/DevExpress.Blazor.Themes/blazing-berry.bs5.min.css" rel="stylesheet" />
 <link href="_content/DevExpress.Blazor.Reporting.Viewer/css/dx-blazor-reporting-components.bs5.css" rel="stylesheet" />
@@ -170,6 +172,14 @@
 
     protected override async Task OnInitializedAsync() {
 
+        if (!string.IsNullOrWhiteSpace(EnvelopeKey)) {
+            var hasAccess = await AuthService.CheckEnvelopeAccessAsync(EnvelopeKey);
+            if (!hasAccess) {
+                Navigation.NavigateTo($"/login/{Uri.EscapeDataString(EnvelopeKey)}");
+                return;
+            }
+        }
+
         if (!AppOptions.Value.ForceToUseFakeDocument && !string.IsNullOrWhiteSpace(EnvelopeKey)) {
             var (pdfBytes, _) = await DocumentService.GetDocumentAsync(EnvelopeKey);
             if (pdfBytes is { Length: > 0 }) {

EnvelopeGenerator.ReceiverUI/Program.cs

@@ -15,6 +15,7 @@ builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.
 builder.Services.Configure<ApiOptions>(opts =>
 builder.Configuration.GetSection(ApiOptions.SectionName).Bind(opts));
 builder.Services.AddScoped<EnvelopeGenerator.ReceiverUI.Services.DocumentService>();
+builder.Services.AddScoped<EnvelopeGenerator.ReceiverUI.Services.AuthService>();
 
 builder.Services.AddDevExpressWebAssemblyBlazorReportViewer();
 builder.Services.AddDevExpressWebAssemblyBlazorPdfViewer();

EnvelopeGenerator.ReceiverUI/Services/AuthService.cs

@@ -0,0 +1,20 @@
+using System.Net;
+using EnvelopeGenerator.ReceiverUI.Options;
+using Microsoft.Extensions.Options;
+
+namespace EnvelopeGenerator.ReceiverUI.Services;
+
+public class AuthService(HttpClient http, IOptions<ApiOptions> apiOptions)
+{
+    private readonly ApiOptions _api = apiOptions.Value;
+
+    /// <summary>
+    /// Checks whether the current user holds a valid receiver token for the given envelope key.
+    /// Calls GET /api/auth/check/envelope/{envelopeKey}.
+    /// </summary>
+    public async Task<bool> CheckEnvelopeAccessAsync(string envelopeKey, CancellationToken cancel = default)
+    {
+        var response = await http.GetAsync($"{_api.BaseUrl}/api/auth/check/envelope/{Uri.EscapeDataString(envelopeKey)}", cancel);
+        return response.StatusCode == HttpStatusCode.OK;
+    }
+}