[JAVA] Google API access token and refresh token

Introduction

The other day, when I used Google's API, I overlooked a Not Found error and a Bad Request error, so I will summarize it as a memo.

Create a project from the Google console

https://console.developers.google.com/apis/dashboard

Creating API credentials

1. OAuth client ID

Select this if the user consents to authorization from the screen

After entering the application type, name, and approved redirect URI, a client ID and client secret were generated.

2. Service account key

Get an access token in JSON format behind the scenes without screen operation. Select this for batch processing

Download the file in JSON format

• Communication using API Client library https://developers.google.com/api-client-library/java/google-api-java-client/oauth2

Obtaining an authorization code

Set client and scoop and access from URL

https://accounts.google.com/o/oauth2/v2/auth?
 scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fdrive.metadata.readonly&
 access_type=offline&
 include_granted_scopes=true&
 redirect_uri=http%3A%2F%2localhost:8080&
 response_type=code&
 client_id=Client ID obtained above

If you agree with Google, you can get the authorization code from the URL. http://localhost:8080/?code=xxxxxxxxxxxx&scope=yyyyyyyyyyy

• 1 You can check the scope at the following URL. https://developers.google.com/identity/protocols/googlescopes
• 2 redirect_uri is the set approved redirect URI
• 3 Access_type can be set to online or offline. offline + You can get refresh_token by accessing the Token API only for the first time.

Obtaining an access token

specification

Point 1: POST method. NG with GET method Point 2: Set "Content-Type: application / x-www-form-urlencoded" in the header. NG if not set or JSON is set.

Sample code

Test.java

        String url = "https://www.googleapis.com/oauth2/v4/token";

		CloseableHttpClient httpclient = HttpClients.createDefault();

		HttpPost request = new HttpPost(url);
		List<BasicNameValuePair> parameters = new ArrayList<BasicNameValuePair>();
		parameters.add(new BasicNameValuePair("code", authorizationCode)); //The authorization code obtained above
		parameters.add(new BasicNameValuePair("client_id", oAuthClientId)); //Client ID for API credentials on the console
		parameters.add(new BasicNameValuePair("client_secret", oAuthClientSecret)); //Client secret of API credentials on the console
		parameters.add(new BasicNameValuePair("redirect_uri", "http://localhost:8080")); //Approved redirect URI that you have set
		parameters.add(new BasicNameValuePair("grant_type", "authorization_code")); //Fixed

		HttpEntity entity = new UrlEncodedFormEntity(parameters);
		request.setEntity(entity);
		
		request.setHeader("Content-Type", "application/x-www-form-urlencoded");

		CloseableHttpResponse response = httpclient.execute(request);
		if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
		    String result = EntityUtils.toString(response.getEntity(), "UTF-8");
		    System.out.println(result);
		}
		response.close();

Response field:

Now that you have the access token, you can get the data from Google. This is an example of setting an access token in the header. curl -H "Authorization: Bearer <access_token>" https://www.googleapis.com/drive/v2/files

Update access token using refresh token

The access token has an expiration date. After a certain period (60 minutes), it becomes invalid. At this time, you may get the authorization code again, It is common to reissue an access token using a refresh token because it is troublesome for the user.

specification

It's the same as an access token.

Sample code

Test.java

        String url = "https://www.googleapis.com/oauth2/v4/token";

		HttpPost request = new HttpPost(url);
		List<BasicNameValuePair> parameters = new ArrayList<BasicNameValuePair>();
		parameters.add(new BasicNameValuePair("refresh_token", "xxxxxxx")); //Refresh token you have
		parameters.add(new BasicNameValuePair("client_id", oAuthClientId)); //Client ID for API credentials on the console
		parameters.add(new BasicNameValuePair("client_secret", oAuthClientSecret)); //Client secret of API credentials on the console
		parameters.add(new BasicNameValuePair("redirect_uri", "http://localhost:8080")); //Approved redirect URI that you have set
		parameters.add(new BasicNameValuePair("grant_type", "refresh_token")); //Fixed

		HttpEntity entity = new UrlEncodedFormEntity(parameters);
		request.setEntity(entity);
		
		request.setHeader("Content-Type", "application/x-www-form-urlencoded");

		CloseableHttpClient httpclient = HttpClients.createDefault();
		CloseableHttpResponse response = httpclient.execute(request);
		if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
		    String result = EntityUtils.toString(response.getEntity(), "UTF-8");
		    System.out.println(result);
		}
		response.close();

This is an example response.

As shown in the sample, there is no refresh token, so if the refresh token is also invalid, you will have to start over from obtaining the authorization code.

Reference URL: https://developers.google.com/identity/protocols/OAuth2WebServer

that's all