Feat/add support for forcing device auth flow on ios (#4944)

* updates to client file writing

* numerous

* minor

* - Align OnLoginSuccess behavior with Android (only call on nil error)
- Remove verbose debug logging from WaitToken in device_flow.go
- Improve TUN FD=0 fallback comments and warning messages
- Document why config save after login differs from Android

* Add nolint directive for staticcheck SA1029 in login.go

* Fix CodeRabbit review issues for iOS/tvOS SDK

- Remove goroutine from OnLoginSuccess callback, invoke synchronously
- Stop treating PermissionDenied as success, propagate as permanent error
- Replace context.TODO() with bounded timeout context (30s) in RequestAuthInfo
- Handle DirectUpdateOrCreateConfig errors in IsLoginRequired and LoginForMobile
- Add permission enforcement to DirectUpdateOrCreateConfig for existing configs
- Fix variable shadowing in device_ios.go where err was masked by := in else block

* Address additional CodeRabbit review issues for iOS/tvOS SDK

- Make tunFd == 0 a hard error with exported ErrInvalidTunnelFD (remove dead fallback code)
- Apply defaults in ConfigFromJSON to prevent partially-initialized configs
- Add nil guards for listener/urlOpener interfaces in public SDK entry points
- Reorder config save before OnLoginSuccess to prevent teardown race
- Add explanatory comment for urlOpener.Open goroutine

* Make urlOpener.Open() synchronous in device auth flow

client/internal/profilemanager/config.go

@@ -3,6 +3,7 @@ package profilemanager
 import (
 	"context"
 	"crypto/tls"
+	"encoding/json"
 	"fmt"
 	"net/url"
 	"os"
@@ -820,3 +821,85 @@ func readConfig(configPath string, createIfMissing bool) (*Config, error) {
 func WriteOutConfig(path string, config *Config) error {
 	return util.WriteJson(context.Background(), path, config)
 }
+
+// DirectWriteOutConfig writes config directly without atomic temp file operations.
+// Use this on platforms where atomic writes are blocked (e.g., tvOS sandbox).
+func DirectWriteOutConfig(path string, config *Config) error {
+	return util.DirectWriteJson(context.Background(), path, config)
+}
+
+// DirectUpdateOrCreateConfig is like UpdateOrCreateConfig but uses direct (non-atomic) writes.
+// Use this on platforms where atomic writes are blocked (e.g., tvOS sandbox).
+func DirectUpdateOrCreateConfig(input ConfigInput) (*Config, error) {
+	if !fileExists(input.ConfigPath) {
+		log.Infof("generating new config %s", input.ConfigPath)
+		cfg, err := createNewConfig(input)
+		if err != nil {
+			return nil, err
+		}
+		err = util.DirectWriteJson(context.Background(), input.ConfigPath, cfg)
+		return cfg, err
+	}
+
+	if isPreSharedKeyHidden(input.PreSharedKey) {
+		input.PreSharedKey = nil
+	}
+
+	// Enforce permissions on existing config files (same as UpdateOrCreateConfig)
+	if err := util.EnforcePermission(input.ConfigPath); err != nil {
+		log.Errorf("failed to enforce permission on config file: %v", err)
+	}
+
+	return directUpdate(input)
+}
+
+func directUpdate(input ConfigInput) (*Config, error) {
+	config := &Config{}
+
+	if _, err := util.ReadJson(input.ConfigPath, config); err != nil {
+		return nil, err
+	}
+
+	updated, err := config.apply(input)
+	if err != nil {
+		return nil, err
+	}
+
+	if updated {
+		if err := util.DirectWriteJson(context.Background(), input.ConfigPath, config); err != nil {
+			return nil, err
+		}
+	}
+
+	return config, nil
+}
+
+// ConfigToJSON serializes a Config struct to a JSON string.
+// This is useful for exporting config to alternative storage mechanisms
+// (e.g., UserDefaults on tvOS where file writes are blocked).
+func ConfigToJSON(config *Config) (string, error) {
+	bs, err := json.MarshalIndent(config, "", "    ")
+	if err != nil {
+		return "", err
+	}
+	return string(bs), nil
+}
+
+// ConfigFromJSON deserializes a JSON string to a Config struct.
+// This is useful for restoring config from alternative storage mechanisms.
+// After unmarshaling, defaults are applied to ensure the config is fully initialized.
+func ConfigFromJSON(jsonStr string) (*Config, error) {
+	config := &Config{}
+	err := json.Unmarshal([]byte(jsonStr), config)
+	if err != nil {
+		return nil, err
+	}
+
+	// Apply defaults to ensure required fields are initialized.
+	// This mirrors what readConfig does after loading from file.
+	if _, err := config.apply(ConfigInput{}); err != nil {
+		return nil, fmt.Errorf("failed to apply defaults to config: %w", err)
+	}
+
+	return config, nil
+}