[[["容易理解","easyToUnderstand","thumb-up"],["確實解決了我的問題","solvedMyProblem","thumb-up"],["其他","otherUp","thumb-up"]],[["難以理解","hardToUnderstand","thumb-down"],["資訊或程式碼範例有誤","incorrectInformationOrSampleCode","thumb-down"],["缺少我需要的資訊/範例","missingTheInformationSamplesINeed","thumb-down"],["翻譯問題","translationIssue","thumb-down"],["其他","otherDown","thumb-down"]],["上次更新時間：2025-09-05 (世界標準時間)。"],[],[],null,["# Accessing data on a user's behalf\n\nWhen your application needs to access data on a user's behalf, this is called a\nthree-legged OAuth flow. In a three-legged OAuth flow, your application obtains\ncredentials from an end user, who signs into their account to complete\nauthentication. Your application then uses the end user's credentials to\naccess Cloud Storage resources on the user's behalf. Here are examples\nof scenarios where this approach can be used:\n\n- Web server applications\n- Installed and desktop applications\n- Mobile applications\n- Client-side JavaScript\n- Applications on limited-input devices\n\nFor more information on these scenarios, see [OAuth 2.0 scenarios](https://developers.google.com/identity/protocols/OAuth2#scenarios).\n\nFor other scenarios, you might want to use [service account credentials](/iam/docs/service-account-overview#credentials).\n\nIf you are designing an application to support multiple authentication options\nfor end users, then use [Firebase Authentication](https://firebase.google.com/docs/auth/), which supports\nemail and password authentication as well as federated sign in with identity\nproviders such as Google, Facebook, Twitter, and GitHub. See\n[Where do I start with Firebase Authentication](https://firebase.google.com/docs/auth/where-to-start)\nfor details on how to set up authentication systems for different use cases.\n\nWhen an application is granted an access token by an end user to access data on\nthe user's behalf, that access token only has the permissions available to the\nuser who grants the token. For example, if jane@example.com has `read-only`\naccess to `example-bucket`, an application which Jane has granted `read-write`\naccess to will be unable to write to `example-bucket` on her behalf.\n\nWhat's next\n-----------\n\n- Learn more about [authentication in Cloud Storage](/storage/docs/authentication)."]]
