Updated sample app to support auth_time

Author: AkshatG6

Samples/Swift/DaysUntilBirthday/Shared/DaysUntilBirthday.swift

@@ -29,6 +29,7 @@ struct DaysUntilBirthday: App {
           GIDSignIn.sharedInstance.restorePreviousSignIn { user, error in
             if let user = user {
               self.authViewModel.state = .signedIn(user)
+              self.authViewModel.authTime = UserDefaults.standard.object(forKey: "authTime") as? Date
             } else if let error = error {
               self.authViewModel.state = .signedOut
               print("There was an error restoring the previous sign-in: \(error)")

Samples/Swift/DaysUntilBirthday/Shared/Services/GoogleSignInAuthenticator.swift

@@ -36,12 +36,14 @@ final class GoogleSignInAuthenticator: ObservableObject {
       return
     }
     let manualNonce = UUID().uuidString
+    let tokenClaims: Set<GIDTokenClaim> = Set([GIDTokenClaim.authTime()])
 
     GIDSignIn.sharedInstance.signIn(
       withPresenting: rootViewController,
       hint: nil,
       additionalScopes: nil,
-      nonce: manualNonce
+      nonce: manualNonce,
+      tokenClaims: tokenClaims
     ) { signInResult, error in
       guard let signInResult = signInResult else {
         print("Error! \(String(describing: error))")
@@ -57,6 +59,10 @@ final class GoogleSignInAuthenticator: ObservableObject {
         assertionFailure("ERROR: Returned nonce doesn't match manual nonce!")
         return
       }
+      if let authTimeDate = self.decodeAuthTime(fromJWT: idToken) {
+        self.authViewModel.authTime = authTimeDate
+        UserDefaults.standard.set(authTimeDate, forKey: "authTime")
+      }
       self.authViewModel.state = .signedIn(signInResult.user)
     }
 
@@ -66,11 +72,27 @@ final class GoogleSignInAuthenticator: ObservableObject {
       return
     }
 
-    GIDSignIn.sharedInstance.signIn(withPresenting: presentingWindow) { signInResult, error in
+    let tokenClaims: Set<GIDTokenClaim> = Set([GIDTokenClaim.authTime()])
+
+    GIDSignIn.sharedInstance.signIn(
+      withPresenting: presentingWindow,
+      tokenClaims: tokenClaims
+      ) { signInResult, error in
       guard let signInResult = signInResult else {
         print("Error! \(String(describing: error))")
         return
       }
+
+      // If the idToken is nil, we cannot get the authTime, so we treat this
+      // as a failure for the app's sign-in flow and return.
+      guard let idToken = signInResult.user.idToken?.tokenString else {
+        print("Error: idToken is missing from signInResult.")
+        return
+      }
+      if let authTimeDate = self.decodeAuthTime(fromJWT: idToken) {
+        self.authViewModel.authTime = authTimeDate
+        UserDefaults.standard.set(authTimeDate, forKey: "authTime")
+      }
       self.authViewModel.state = .signedIn(signInResult.user)
     }
 #endif
@@ -154,6 +176,16 @@ private extension GoogleSignInAuthenticator {
     return nonce
   }
 
+  func decodeAuthTime(fromJWT jwt: String) -> Date? {
+    let segments = jwt.components(separatedBy: ".")
+    guard segments.count > 1,
+          let parts = decodeJWTSegment(segments[1]),
+          let authTimeInterval = parts["auth_time"] as? TimeInterval else {
+      return nil
+    }
+    return Date(timeIntervalSince1970: authTimeInterval)
+  }
+
   func decodeJWTSegment(_ segment: String) -> [String: Any]? {
     guard let segmentData = base64UrlDecode(segment),
           let segmentJSON = try? JSONSerialization.jsonObject(with: segmentData, options: []),

Samples/Swift/DaysUntilBirthday/Shared/ViewModels/AuthenticationViewModel.swift

@@ -22,6 +22,7 @@ final class AuthenticationViewModel: ObservableObject {
   /// The user's log in status.
   /// - note: This will publish updates when its value changes.
   @Published var state: State
+  @Published var authTime: Date?
   private var authenticator: GoogleSignInAuthenticator {
     return GoogleSignInAuthenticator(authViewModel: self)
   }
@@ -69,7 +70,13 @@ final class AuthenticationViewModel: ObservableObject {
   @MainActor func addBirthdayReadScope(completion: @escaping () -> Void) {
       authenticator.addBirthdayReadScope(completion: completion)
   }
-
+  
+  var formattedAuthTimeString: String? {
+          guard let date = authTime else { return nil }
+          let formatter = DateFormatter()
+          formatter.dateFormat = "dd/MM/yyyy"
+          return formatter.string(from: date)
+  }
 }
 
 extension AuthenticationViewModel {

Samples/Swift/DaysUntilBirthday/iOS/UserProfileView.swift

@@ -35,6 +35,9 @@ struct UserProfileView: View {
               Text(userProfile.name)
                 .font(.headline)
               Text(userProfile.email)
+              if let authTimeString = authViewModel.formattedAuthTimeString {
+                  Text("Last sign-in date: \(authTimeString)")
+              }
             }
           }
           NavigationLink(NSLocalizedString("View Days Until Birthday", comment: "View birthday days"),

Samples/Swift/DaysUntilBirthday/macOS/UserProfileView.swift

@@ -19,6 +19,9 @@ struct UserProfileView: View {
               Text(userProfile.name)
                 .font(.headline)
               Text(userProfile.email)
+              if let authTimeString = authViewModel.formattedAuthTimeString {
+                  Text("Last sign-in date: \(authTimeString)")
+              }
             }
           }
           Button(NSLocalizedString("Sign Out", comment: "Sign out button"), action: signOut)