disallowed_useragent 🔐 Authentication

Google OAuth: Error 403: disallowed_useragent (sign-in from an embedded WebView)

Google blocks OAuth sign-in inside embedded WebViews (in-app browsers, Electron BrowserWindow, React Native WebView).

Seen on: REST API

Meaning

Google requires the system browser or Custom Tabs/ASWebAuthenticationSession for OAuth. In-app browsers of social apps (Instagram, Facebook) also trigger it when users open your site there.

Common causes

  • OAuth inside WKWebView/Android WebView/Electron
  • Link opened in Instagram/Facebook/LinkedIn in-app browser
  • Custom user agent spoofing

⚡ Quick fix

  1. Use AppAuth / ASWebAuthenticationSession / Custom Tabs
  2. In web apps, detect in-app browsers and ask users to open in the system browser
  3. Use Google’s native sign-in SDKs

Detailed fix by platform

Swift

  1. bash
    let session = ASWebAuthenticationSession(url: authURL, callbackURLScheme: "com.example.app") { url, error in /* handle */ }
session.presentationContextProvider = self
session.start()

How to diagnose

  1. Context — WebView or system browser?
  2. Source — In-app browser of another app?

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