what does State means in Google Drive OAuth 2.0 API - oauth

Question

Hell.
In the documentation of google drive SDK, it is not mentioned what does setState create.
I'm going to implement Google drive Server-side Authorization. I found the code in documentation.
import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeRequestUrl;
import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets;
import com.google.api.client.googleapis.auth.oauth2.GoogleTokenResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.jackson.JacksonFactory;
import com.google.api.services.oauth2.Oauth2;
import com.google.api.services.oauth2.model.Userinfo;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
// ...
class MyClass {
// Path to client_secrets.json which should contain a JSON document such as:
// {
// "web": {
// "client_id": "[[YOUR_CLIENT_ID]]",
// "client_secret": "[[YOUR_CLIENT_SECRET]]",
// "auth_uri": "https://accounts.google.com/o/oauth2/auth",
// "token_uri": "https://accounts.google.com/o/oauth2/token"
// }
// }
private static final String CLIENTSECRETS_LOCATION = "client_secrets.json";
private static final String REDIRECT_URI = "<YOUR_REGISTERED_REDIRECT_URI>";
private static final List<String> SCOPES = Arrays.asList(
"https://www.googleapis.com/auth/drive.file",
"https://www.googleapis.com/auth/userinfo.email",
"https://www.googleapis.com/auth/userinfo.profile");
private static GoogleAuthorizationCodeFlow flow = null;
/**
* Exception thrown when an error occurred while retrieving credentials.
*/
public static class GetCredentialsException extends Exception {
protected String authorizationUrl;
/**
* Construct a GetCredentialsException.
*
* #param authorizationUrl The authorization URL to redirect the user to.
*/
public GetCredentialsException(String authorizationUrl) {
this.authorizationUrl = authorizationUrl;
}
/**
* Set the authorization URL.
*/
public void setAuthorizationUrl(String authorizationUrl) {
this.authorizationUrl = authorizationUrl;
}
/**
* #return the authorizationUrl
*/
public String getAuthorizationUrl() {
return authorizationUrl;
}
}
/**
* Exception thrown when a code exchange has failed.
*/
public static class CodeExchangeException extends GetCredentialsException {
/**
* Construct a CodeExchangeException.
*
* #param authorizationUrl The authorization URL to redirect the user to.
*/
public CodeExchangeException(String authorizationUrl) {
super(authorizationUrl);
}
}
/**
* Exception thrown when no refresh token has been found.
*/
public static class NoRefreshTokenException extends GetCredentialsException {
/**
* Construct a NoRefreshTokenException.
*
* #param authorizationUrl The authorization URL to redirect the user to.
*/
public NoRefreshTokenException(String authorizationUrl) {
super(authorizationUrl);
}
}
/**
* Exception thrown when no user ID could be retrieved.
*/
private static class NoUserIdException extends Exception {
}
/**
* Retrieved stored credentials for the provided user ID.
*
* #param userId User's ID.
* #return Stored Credential if found, {#code null} otherwise.
*/
static Credential getStoredCredentials(String userId) {
// TODO: Implement this method to work with your database. Instantiate a new
// Credential instance with stored accessToken and refreshToken.
throw new UnsupportedOperationException();
}
/**
* Store OAuth 2.0 credentials in the application's database.
*
* #param userId User's ID.
* #param credentials The OAuth 2.0 credentials to store.
*/
static void storeCredentials(String userId, Credential credentials) {
// TODO: Implement this method to work with your database.
// Store the credentials.getAccessToken() and credentials.getRefreshToken()
// string values in your database.
throw new UnsupportedOperationException();
}
/**
* Build an authorization flow and store it as a static class attribute.
*
* #return GoogleAuthorizationCodeFlow instance.
* #throws IOException Unable to load client_secrets.json.
*/
static GoogleAuthorizationCodeFlow getFlow() throws IOException {
if (flow == null) {
HttpTransport httpTransport = new NetHttpTransport();
JacksonFactory jsonFactory = new JacksonFactory();
GoogleClientSecrets clientSecrets =
GoogleClientSecrets.load(jsonFactory,
MyClass.class.getResourceAsStream(CLIENTSECRETS_LOCATION));
flow =
new GoogleAuthorizationCodeFlow.Builder(httpTransport, jsonFactory, clientSecrets, SCOPES)
.setAccessType("offline").setApprovalPrompt("force").build();
}
return flow;
}
/**
* Exchange an authorization code for OAuth 2.0 credentials.
*
* #param authorizationCode Authorization code to exchange for OAuth 2.0
* credentials.
* #return OAuth 2.0 credentials.
* #throws CodeExchangeException An error occurred.
*/
static Credential exchangeCode(String authorizationCode)
throws CodeExchangeException {
try {
GoogleAuthorizationCodeFlow flow = getFlow();
GoogleTokenResponse response =
flow.newTokenRequest(authorizationCode).setRedirectUri(REDIRECT_URI).execute();
return flow.createAndStoreCredential(response, null);
} catch (IOException e) {
System.err.println("An error occurred: " + e);
throw new CodeExchangeException(null);
}
}
/**
* Send a request to the UserInfo API to retrieve the user's information.
*
* #param credentials OAuth 2.0 credentials to authorize the request.
* #return User's information.
* #throws NoUserIdException An error occurred.
*/
static Userinfo getUserInfo(Credential credentials)
throws NoUserIdException {
Oauth2 userInfoService =
new Oauth2.Builder(new NetHttpTransport(), new JacksonFactory(), credentials).build();
Userinfo userInfo = null;
try {
userInfo = userInfoService.userinfo().get().execute();
} catch (IOException e) {
System.err.println("An error occurred: " + e);
}
if (userInfo != null && userInfo.getId() != null) {
return userInfo;
} else {
throw new NoUserIdException();
}
}
/**
* Retrieve the authorization URL.
*
* #param emailAddress User's e-mail address.
* #param state State for the authorization URL.
* #return Authorization URL to redirect the user to.
* #throws IOException Unable to load client_secrets.json.
*/
public static String getAuthorizationUrl(String emailAddress, String state) throws IOException {
GoogleAuthorizationCodeRequestUrl urlBuilder =
getFlow().newAuthorizationUrl().setRedirectUri(REDIRECT_URI).setState(state);
urlBuilder.set("user_id", emailAddress);
return urlBuilder.build();
}
/**
* Retrieve credentials using the provided authorization code.
*
* This function exchanges the authorization code for an access token and
* queries the UserInfo API to retrieve the user's e-mail address. If a
* refresh token has been retrieved along with an access token, it is stored
* in the application database using the user's e-mail address as key. If no
* refresh token has been retrieved, the function checks in the application
* database for one and returns it if found or throws a NoRefreshTokenException
* with the authorization URL to redirect the user to.
*
* #param authorizationCode Authorization code to use to retrieve an access
* token.
* #param state State to set to the authorization URL in case of error.
* #return OAuth 2.0 credentials instance containing an access and refresh
* token.
* #throws NoRefreshTokenException No refresh token could be retrieved from
* the available sources.
* #throws IOException Unable to load client_secrets.json.
*/
public static Credential getCredentials(String authorizationCode, String state)
throws CodeExchangeException, NoRefreshTokenException, IOException {
String emailAddress = "";
try {
Credential credentials = exchangeCode(authorizationCode);
Userinfo userInfo = getUserInfo(credentials);
String userId = userInfo.getId();
emailAddress = userInfo.getEmail();
if (credentials.getRefreshToken() != null) {
storeCredentials(userId, credentials);
return credentials;
} else {
credentials = getStoredCredentials(userId);
if (credentials != null && credentials.getRefreshToken() != null) {
return credentials;
}
}
} catch (CodeExchangeException e) {
e.printStackTrace();
// Drive apps should try to retrieve the user and credentials for the current
// session.
// If none is available, redirect the user to the authorization URL.
e.setAuthorizationUrl(getAuthorizationUrl(emailAddress, state));
throw e;
} catch (NoUserIdException e) {
e.printStackTrace();
}
// No refresh token has been retrieved.
String authorizationUrl = getAuthorizationUrl(emailAddress, state);
throw new NoRefreshTokenException(authorizationUrl);
}
}
First here, I should invoke getCredentials method, which has 2 parameters - Authorization code and State. here, what should state be? where can I get this? what does this means?

Answer 1

It allows to you pass an arbitrary string to consent page, and when consent page is redirecting back to your application it keeps the state as a query parameter. It's usually used to keep information about the next page and the state of the page.
If you dont have a state to keep for post-redirect, you can pass null.