Simple Google-OAuth2 from a Java client

OAuth is a powerful way to ensure that clients have access to appropriate resources, and the Google OAuth libs do a lot of the heavy lifting for you. But while the doco is pretty good I found it lacking when looking for the most appropriate way to authorize for a simple Java (non-web) application and that's probably to do with the rate at which this area is moving.

It turns out that there are excellent classes in the Google libraries to make OAuth absolutely trivial, in fact it's really only 3 lines:

1. Construct your AuthorizationCodeFlow
2. Construct your AuthorizationCodeInstalledApp
3. Ask the InstalledApp to authorize the client

Here's the full code listing:
// If you need a local proxy (eg for getting out from behind a corporate firewall) final Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(PROXY_HOST, PROXY_PORT)); final HttpTransport httpTransport = new NetHttpTransport.Builder().setProxy(proxy).build(); final JsonFactory jsonFactory = new JacksonFactory(); final java.io.File credentialFile = new java.io.File(System.getProperty("user.home") + CREDENTIAL_STORE_FILE_NAME); final CredentialStore credentialStore = new FileCredentialStore(credentialFile, jsonFactory); final AuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder( httpTransport, jsonFactory, CLIENT_ID, CLIENT_SECRET, Arrays.asList(DriveScopes.DRIVE)) // Need "offline" and "force" in order to ensure we get a URL that will return a refresh_token too. .setAccessType("offline") .setApprovalPrompt("force") .setCredentialStore(credentialStore) .build(); // Retrieves a valid credential. It refreshes the access_token if required // and prompts the user (opening a browser page pointing at the appropriate auth page) for auth token if required. // and then persists the returned credentials to our CredentialStore final AuthorizationCodeInstalledApp app = new AuthorizationCodeInstalledApp(flow, new GooglePromptReceiver()); final Credential credential = app.authorize(CLIENT_ID); // Now do something with the new authorized client like access Google Drive final Drive service = new Drive.Builder(httpTransport, jsonFactory, credential) .setApplicationName("MyCoolApp") .build();

Now to make this happen you're going to need to include the relevant Google libs. You can find lots of good info about the libs here google-api-java-client, google-oauth-java-client and google-http-java-client.

The libs necessary for the above are:
<repositories> <repository> <id>google-api-services</id> <url>http://mavenrepo.google-api-java-client.googlecode.com/hg</url> </repository> </repositories> <dependencies> <dependency> <groupId>com.google.apis</groupId> <artifactId>google-api-services-drive</artifactId> <version>v2-rev9-1.8.0-beta</version> </dependency> <dependency> <groupId>com.google.api-client</groupId> <artifactId>google-api-client-java6</artifactId> <version>1.13.2-beta</version> </dependency> <dependency> <groupId>com.google.http-client</groupId> <artifactId>google-http-client-jackson</artifactId> <version>1.13.1-beta</version> </dependency> <dependency> <groupId>com.google.oauth-client</groupId> <artifactId>google-oauth-client-java6</artifactId> <version>1.13.1-beta</version> </dependency> </dependencies>