# OAuth 2.0 and the Google OAuth Client Library for Java

[TOC]

###### tags: `oauth` `google` `java`

---

## Authorization Code Flow for Browser-based Client[🔗](https://developers.google.com/api-client-library/java/google-oauth-java-client/oauth2#browser-based_client_flow)

> These are the typical steps of the the browser-based client flow specified in the Implicit Grant specification:
>
> - Using `BrowserClientRequestUrl`, redirect the end user's browser to the authorization page where the end user can grant your application access to their protected data.
> - Use a JavaScript application to process the access token found in the URL fragment at the redirect URI that is registered with the authorization server.
>
> Sample usage for a web application:

public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
	String url = new BrowserClientRequestUrl(
		"https://server.example.com/authorize",
		"s6BhdRkqt3"
	).
		setState("xyz").
		setRedirectUri("https://client.example.com/cb").
		build();

	response.sendRedirect(url);
}

## Detecting an expired access token[🔗](https://developers.google.com/api-client-library/java/google-oauth-java-client/oauth2#detecting_an_expired_access_token)

> According to the OAuth 2.0 bearer specification, when the server is called to access a protected resource with an expired access token, the server typically responds with an HTTP 401 Unauthorized status code such as the following:

(未完 待續)