Great question—these two Chrome Identity APIs often get mixed up, but they serve distinct purposes depending on your authentication needs. Let’s break this down clearly:

1. Core Purpose & Use Case #

• chrome.identity.getAuthToken(): This is a Google Account-specific API tightly integrated with Chrome’s built-in account system. Use it when you need to authenticate users with their existing Chrome-linked Google accounts, or to fetch OAuth 2.0 tokens for calling Google services (like Drive, Gmail, or Calendar APIs). Its primary goal is to minimize user friction—if the user is already signed into Chrome and has previously granted your extension permissions, it’ll return a token instantly without any extra steps.
• chrome.identity.launchWebAuthFlow(): This is a universal OAuth 2.0/OpenID Connect tool that works with any standards-compliant identity provider (GitHub, Facebook, custom OAuth servers, etc.). It’s not tied to Chrome’s account system; instead, it launches a browser window to guide users through the third-party provider’s full authentication flow, then returns an authorization code or token to your extension.

2. Integration with Chrome’s Account System #

• getAuthToken(): Deeply integrated with Chrome’s account manager. It automatically uses the user’s currently logged-in Google account (you can specify a specific account via the account parameter) and caches valid tokens for future calls. If a token expires, Chrome will automatically refresh it (as long as your extension has refresh permissions).
• launchWebAuthFlow(): Completely independent of Chrome’s account system. Every call triggers the full third-party auth flow (unless the provider has its own session caching), which might require users to re-enter credentials or re-authorize even if they’re signed into that provider via Chrome.

3. Token Handling & Scope #

• getAuthToken(): Returns a Google OAuth 2.0 access token that only works with Google’s APIs. Token refresh is handled automatically by Chrome—you don’t need to write custom refresh logic. You must declare the specific Google API permissions (e.g., "https://www.googleapis.com/auth/drive.readonly") in your extension’s manifest.
• launchWebAuthFlow(): Returns an authorization code or token issued by your chosen provider, usable with any service that supports OAuth 2.0. You’re responsible for all token management: storing it, handling expiration, and implementing refresh logic yourself.

4. User Experience #

• getAuthToken(): Offers a seamless experience by reusing Chrome’s existing login state. If the user has already authorized your extension, it’s nearly invisible. If not, it shows a compact, Chrome-native permission prompt instead of redirecting to an external website.
• launchWebAuthFlow(): Launches a standalone browser window loading the provider’s login/authorization page, mirroring the OAuth flow users see on regular websites.

Why does getAuthToken() sometimes launch an auth flow? #

This is a common behavior, and it happens in a few key scenarios:

• First-time authorization: If your extension is requesting tokens for the first time, or the user previously revoked your extension’s permissions, Chrome will show its native permission prompt to let the user confirm access to the requested Google API scopes.
• No valid tokens available: If the cached access token has expired and Chrome can’t automatically refresh it (e.g., the refresh token is invalid, or your extension doesn’t have refresh permissions), it will re-initiate the authorization flow.
• New permissions added: If you update your extension’s manifest to include additional Google API scopes, Chrome will prompt the user to approve these new permissions even if they’ve authorized your extension before.
• No active Google account: If the user isn’t signed into any Google account in Chrome, getAuthToken() will first guide them to sign in, then proceed with authorization.

In short: getAuthToken() is a "shortcut" for Google Account authentication, while launchWebAuthFlow() is a flexible tool for any third-party auth system. The auth flow triggered by getAuthToken() is just a fallback for when it can’t reuse an existing valid session or permission grant.

内容的提问来源于stack exchange，提问作者Alexander Mills