Removed the logic for saving auth_time within User Defaults. Added the logic for decoding id token within AuthenticationViewModel

Author: AkshatG6

Samples/Swift/DaysUntilBirthday/Shared/DaysUntilBirthday.swift

@@ -29,7 +29,6 @@ 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

@@ -59,10 +59,6 @@ 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)
     }
 
@@ -80,17 +76,6 @@ final class GoogleSignInAuthenticator: ObservableObject {
         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
@@ -164,7 +149,7 @@ final class GoogleSignInAuthenticator: ObservableObject {
 
 // MARK: Parse nonce from JWT ID Token
 
-private extension GoogleSignInAuthenticator {
+extension GoogleSignInAuthenticator {
   func decodeNonce(fromJWT jwt: String) -> String? {
     let segments = jwt.components(separatedBy: ".")
     guard let parts = decodeJWTSegment(segments[1]),
@@ -174,16 +159,6 @@ 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

@@ -22,10 +22,21 @@ 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)
   }
+
+  // 3. Change authTime to a computed property
+  var authTime: Date? {
+    switch state {
+    case .signedIn(let user):
+      guard let idToken = user.idToken?.tokenString else { return nil }
+      return decodeAuthTime(fromJWT: idToken)
+    case .signedOut:
+      return nil
+    }
+  }
+
   /// The user-authorized scopes.
   /// - note: If the user is logged out, then this will default to empty.
   var authorizedScopes: [String] {
@@ -79,6 +90,42 @@ final class AuthenticationViewModel: ObservableObject {
   }
 }
 
+private extension AuthenticationViewModel {
+    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: []),
+              let payload = segmentJSON as? [String: Any] else {
+            return nil
+        }
+        return payload
+    }
+
+    func base64UrlDecode(_ value: String) -> Data? {
+        var base64 = value
+            .replacingOccurrences(of: "-", with: "+")
+            .replacingOccurrences(of: "_", with: "/")
+
+        let length = Double(base64.lengthOfBytes(using: String.Encoding.utf8))
+        let requiredLength = 4 * ceil(length / 4.0)
+        let paddingLength = requiredLength - length
+        if paddingLength > 0 {
+            let padding = "".padding(toLength: Int(paddingLength), withPad: "=", startingAt: 0)
+            base64 = base64 + padding
+        }
+        return Data(base64Encoded: base64, options: .ignoreUnknownCharacters)
+    }
+}
+
 extension AuthenticationViewModel {
   /// An enumeration representing logged in status.
   enum State {