feat(apple): Show UI alerts for sign in failures (#7838)

On Apple, we will silently fail if the tunnel fails to start. This adds
a simple `NSAlert` modal (macOS) or `Alert` popup (iOS) that must be
dismissed before continuing if the tunnel fails to come up, so that the
user has a chance of understanding why.

The vast majority of the time this fails due to DNS lookup errors while
starting connlib.

Related: #7004
Supersedes: #7814

swift/apple/Firezone/Application/FirezoneApp.swift

@@ -16,6 +16,7 @@ struct FirezoneApp: App {
   @StateObject var favorites: Favorites
   @StateObject var appViewModel: AppViewModel
   @StateObject var store: Store
+  @StateObject private var errorHandler = GlobalErrorHandler()
 
   init() {
     // Initialize Telemetry as early as possible
@@ -35,7 +36,7 @@ struct FirezoneApp: App {
   var body: some Scene {
 #if os(iOS)
     WindowGroup {
-      AppView(model: appViewModel)
+      AppView(model: appViewModel).environmentObject(errorHandler)
     }
 #elseif os(macOS)
     WindowGroup(

swift/apple/FirezoneKit/Sources/FirezoneKit/Managers/VPNConfigurationManager.swift

@@ -271,7 +271,7 @@ public class VPNConfigurationManager {
     Telemetry.setEnvironmentOrClose(settings.apiURL)
   }
 
-  func start(token: String? = nil) {
+  func start(token: String? = nil) throws {
     var options: [String: NSObject] = [:]
 
     // Pass token if provided
@@ -285,11 +285,7 @@ public class VPNConfigurationManager {
       options.merge(["id": id as NSObject]) { _, n in n }
     }
 
-    do {
-      try session()?.startTunnel(options: options)
-    } catch {
-      Log.error(error)
-    }
+    try session()?.startTunnel(options: options)
   }
 
   func stop(clearToken: Bool = false) {

swift/apple/FirezoneKit/Sources/FirezoneKit/Models/AuthClient.swift

@@ -9,10 +9,24 @@ import Foundation
 
 enum AuthClientError: Error {
   case invalidCallbackURL
-  case invalidStateReturnedInCallback(expected: String, got: String)
-  case authResponseError(Error)
-  case sessionFailure(Error)
   case randomNumberGenerationFailure(errorStatus: Int32)
+
+  var description: String {
+    switch self {
+    case .invalidCallbackURL:
+      return """
+      Invalid callback URL. Please try signing in again.
+      If this issue persists, contact your administrator.
+      """
+    case .randomNumberGenerationFailure(let errorStatus):
+      return """
+      Could not generate secure sign in params. Please try signing in again.
+      If this issue persists, contact your administrator.
+
+      Code: \(errorStatus)
+      """
+    }
+  }
 }
 
 struct AuthClient {

swift/apple/FirezoneKit/Sources/FirezoneKit/Models/WebAuthSession.swift

@@ -8,14 +8,13 @@
 import Foundation
 import AuthenticationServices
 
-
 /// Wraps the ASWebAuthenticationSession ordeal so it can be called from either
 /// the AuthView (iOS) or the MenuBar (macOS)
 @MainActor
 struct WebAuthSession {
   private static let scheme = "firezone-fd0020211111"
 
-  static func signIn(store: Store) {
+  static func signIn(store: Store) async throws {
     guard let authURL = store.authURL(),
           let authClient = try? AuthClient(authURL: authURL),
           let url = try? authClient.build()
@@ -23,32 +22,37 @@ struct WebAuthSession {
 
     let anchor = PresentationAnchor()
 
-    let session = ASWebAuthenticationSession(url: url, callbackURLScheme: scheme) { returnedURL, error in
-      guard error == nil,
-            let authResponse = try? authClient.response(url: returnedURL)
-      else {
-        // Can happen if the user closes the opened Webview without signing in
-        dump(error)
-        return
-      }
-
-      Task {
+    let authResponse = try await withCheckedThrowingContinuation() { continuation in
+      let session = ASWebAuthenticationSession(url: url, callbackURLScheme: scheme) {
+ returnedURL,
+ error in
         do {
-          try await store.signIn(authResponse: authResponse)
+          if let error = error as? ASWebAuthenticationSessionError,
+             error.code == .canceledLogin {
+            // User canceled sign in
+          } else if let error = error {
+            throw error
+          }
+
+          let authResponse = try authClient.response(url: returnedURL)
+
+          continuation.resume(returning: authResponse)
         } catch {
-          Log.error(error)
+          continuation.resume(throwing: error)
         }
       }
+
+      // Apple weirdness, doesn't seem to be actually used in macOS
+      session.presentationContextProvider = anchor
+
+      // load cookies
+      session.prefersEphemeralWebBrowserSession = false
+
+      // Start auth
+      session.start()
     }
 
-    // Apple weirdness, doesn't seem to be actually used in macOS
-    session.presentationContextProvider = anchor
-
-    // load cookies
-    session.prefersEphemeralWebBrowserSession = false
-
-    // Start auth
-    session.start()
+    try await store.signIn(authResponse: authResponse)
   }
 }
 

swift/apple/FirezoneKit/Sources/FirezoneKit/Stores/Store.swift

@@ -55,7 +55,10 @@ public final class Store: ObservableObject {
   private func initNotifications() {
     // Finish initializing notification binding
     sessionNotification.signInHandler = {
-      WebAuthSession.signIn(store: self)
+      Task.detached {
+        do { try await WebAuthSession.signIn(store: self) }
+        catch { Log.error(error) }
+      }
     }
 
     sessionNotification.$decision
@@ -173,14 +176,14 @@ public final class Store: ObservableObject {
     return URL(string: settings.authBaseURL)
   }
 
-  func start(token: String? = nil) async throws {
+  private func start(token: String? = nil) throws {
     guard status == .disconnected
     else {
       Log.log("\(#function): Already connected")
       return
     }
 
-    self.vpnConfigurationManager.start(token: token)
+    try self.vpnConfigurationManager.start(token: token)
   }
 
   func stop(clearToken: Bool = false) {
@@ -198,7 +201,7 @@ public final class Store: ObservableObject {
     try await self.vpnConfigurationManager.saveAuthResponse(authResponse)
 
     // Bring the tunnel up and send it a token to start
-    self.vpnConfigurationManager.start(token: authResponse.token)
+    try self.vpnConfigurationManager.start(token: authResponse.token)
   }
 
   func signOut() async throws {

swift/apple/FirezoneKit/Sources/FirezoneKit/Views/AppView.swift

@@ -55,7 +55,7 @@ public class AppViewModel: ObservableObject {
         if vpnConfigurationStatus == .disconnected {
 
           // Try to connect on start
-          await self.store.vpnConfigurationManager.start()
+          try await self.store.vpnConfigurationManager.start()
         }
       } catch {
         Log.error(error)

swift/apple/FirezoneKit/Sources/FirezoneKit/Views/GlobalErrorHandler.swift

@@ -0,0 +1,33 @@
+//
+//  GlobalErrorHandler.swift
+//  (c) 2024 Firezone, Inc.
+//  LICENSE: Apache-2.0
+//
+
+// A utility class for responding to errors raised in the view hierarchy.
+
+import SwiftUI
+
+public class ErrorAlert: Identifiable {
+  var title: String
+  var error: Error
+
+  public init(title: String = "An error occurred", error: Error) {
+    self.title = title
+    self.error = error
+  }
+}
+
+public class GlobalErrorHandler: ObservableObject {
+  @Published var currentAlert: ErrorAlert?
+
+  public init() {}
+
+  public func handle(_ errorAlert: ErrorAlert) {
+    currentAlert = errorAlert
+  }
+
+  public func clear() {
+    currentAlert = nil
+  }
+}

swift/apple/FirezoneKit/Sources/FirezoneKit/Views/MenuBar.swift

@@ -261,7 +261,21 @@ public final class MenuBar: NSObject, ObservableObject {
   }
 
   @objc private func signInButtonTapped() {
-    WebAuthSession.signIn(store: model.store)
+    Task.detached {
+      do {
+        try await WebAuthSession.signIn(store: self.model.store)
+      } catch {
+        Log.error(error)
+
+        let alert = await NSAlert()
+        await MainActor.run {
+          alert.messageText = "Error signing in"
+          alert.informativeText = error.localizedDescription
+          alert.alertStyle = .warning
+          let _ = alert.runModal()
+        }
+      }
+    }
   }
 
   @objc private func signOutButtonTapped() {

swift/apple/FirezoneKit/Sources/FirezoneKit/Views/WelcomeView.swift

@@ -15,13 +15,10 @@ final class WelcomeViewModel: ObservableObject {
   init(store: Store) {
     self.store = store
   }
-
-  func signInButtonTapped() {
-    WebAuthSession.signIn(store: store)
-  }
 }
 
 struct WelcomeView: View {
+  @EnvironmentObject var errorHandler: GlobalErrorHandler
   @ObservedObject var model: WelcomeViewModel
 
   var body: some View {
@@ -41,11 +38,25 @@ struct WelcomeView: View {
         """).multilineTextAlignment(.center)
           .padding(.bottom, 10)
         Button("Sign in") {
-          model.signInButtonTapped()
+          Task.detached {
+            do {
+              try await WebAuthSession.signIn(store: model.store)
+            } catch {
+              Log.error(error)
+
+              await MainActor.run {
+                self.errorHandler.handle(ErrorAlert(
+                  title: "Error signing in",
+                  error: error
+                ))
+              }
+            }
+          }
         }
         .buttonStyle(.borderedProminent)
         .controlSize(.large)
         Spacer()
-      })
+      }
+    )
   }
 }

swift/apple/FirezoneKit/Sources/FirezoneKit/Views/iOSNavigationView.swift

@@ -13,6 +13,7 @@ struct iOSNavigationView<Content: View>: View {
   @State private var isSettingsPresented = false
   @ObservedObject var model: AppViewModel
   @Environment(\.openURL) var openURL
+  @EnvironmentObject var errorHandler: GlobalErrorHandler
 
   let content: Content
 
@@ -25,8 +26,19 @@ struct iOSNavigationView<Content: View>: View {
     NavigationView {
       content
         .navigationBarTitleDisplayMode(.inline)
-        .navigationBarItems(leading: AuthMenu)
-        .navigationBarItems(trailing: SettingsButton)
+        .navigationBarItems(leading: AuthMenu, trailing: SettingsButton)
+        .alert(
+          item: $errorHandler.currentAlert,
+          content: { alert in
+            Alert(
+              title: Text(alert.title),
+              message: Text(alert.error.localizedDescription),
+              dismissButton: .default(Text("OK")) {
+                errorHandler.clear()
+              }
+            )
+          }
+        )
     }
     .sheet(isPresented: $isSettingsPresented) {
       SettingsView(favorites: model.favorites, model: SettingsViewModel(store: model.store))
@@ -54,7 +66,22 @@ struct iOSNavigationView<Content: View>: View {
         }
       } else {
         Button(action: {
-          WebAuthSession.signIn(store: model.store)
+          Task.detached {
+            do {
+              try await WebAuthSession.signIn(store: model.store)
+            } catch {
+              Log.error(error)
+
+              await MainActor.run {
+                self.errorHandler.handle(
+                  ErrorAlert(
+                    title: "Error signing in",
+                    error: error
+                  )
+                )
+              }
+            }
+          }
         }) {
           Label("Sign in", systemImage: "person.crop.circle.fill.badge.plus")
         }