Google OAuth 2.0 client ID authorization via embedded webview

Google OAuth 2.0 Client ID Authorization via Embedded Webview

Introduction

This article delves into the process of authenticating your application using Google OAuth 2.0 by embedding a webview within your native application. This method empowers users to log in to Google accounts directly within your app, offering a seamless and integrated experience.

Understanding Google OAuth 2.0

Google OAuth 2.0 is a robust authorization framework that enables third-party applications to access user data from Google services (like Google Drive, Gmail, YouTube, etc.) without requiring their passwords. This approach promotes security and privacy by allowing users to grant specific permissions to applications while maintaining control over their account information.

Setting Up Your Google Cloud Project

1. Visit the Google Cloud Console (https://console.cloud.google.com/) and create a new project or select an existing one.
2. Navigate to the “APIs & Services” section and enable the “Google OAuth API”.
3. Under “Credentials,” click “Create credentials” and choose “OAuth client ID”.
4. Select “Application type” as “Android” (or your respective platform) and provide the required details (app package name, SHA-1 fingerprint, etc.).
5. Download the generated JSON file containing your client ID and secret. Securely store this file within your application.

Implementing the Webview

Here’s how to embed a webview and initiate the authorization process:

1. Include the webview library in your project.
2. Create a webview instance and load the Google authorization URL:

<webview
    android:id="@+id/webview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginTop="10dp" />

String clientId = "YOUR_CLIENT_ID"; // Replace with your client ID
String redirectUri = "YOUR_REDIRECT_URI"; // Replace with your redirect URI
String scopes = "profile email"; // Specify the required scopes

String authUrl = "https://accounts.google.com/o/oauth2/v2/auth" +
                "?client_id=" + clientId +
                "&redirect_uri=" + redirectUri +
                "&response_type=code" +
                "&scope=" + scopes;

webview.loadUrl(authUrl);

Handling the Redirect

After the user authenticates, Google redirects to your specified “redirect URI”. You need to intercept this redirect within your webview:

webview.setWebViewClient(new WebViewClient() {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        if (url.startsWith(redirectUri)) {
            // Extract the authorization code from the URL
            String code = Uri.parse(url).getQueryParameter("code");
            // Proceed with the token exchange process (see below)
            return true; // Prevent the webview from loading the redirect URL
        }
        return false; // Allow other URL loads
    }
});

Token Exchange

Once you have the authorization code, you can exchange it for an access token using your client ID and secret:

String tokenUrl = "https://oauth2.googleapis.com/token";
String tokenRequest = "grant_type=authorization_code" +
        "&client_id=" + clientId +
        "&client_secret=" + clientSecret +
        "&redirect_uri=" + redirectUri +
        "&code=" + code;

// Make a POST request to the token URL with the token request
// You can use libraries like Volley, Retrofit, or OkHttp for this
// Example using Volley:
// ...

JsonObjectRequest tokenRequest = new JsonObjectRequest(Request.Method.POST, tokenUrl, null,
        new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                // Extract the access token from the response
                String accessToken = response.getString("access_token");
                // Now you can use the access token to access user data
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                // Handle errors
            }
        }) {
        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String, String> headers = new HashMap<String, String>();
            headers.put("Content-Type", "application/x-www-form-urlencoded");
            return headers;
        }
    };

queue.add(tokenRequest);

Using the Access Token

You can now use the access token to access Google APIs on behalf of the user. Each API has its own documentation specifying the required headers and endpoint URLs for making requests. Typically, you would include the access token in the Authorization header of your requests:

// Example: Making a request to the Google People API
String apiUrl = "https://people.googleapis.com/v1/people/me";
String accessToken = "YOUR_ACCESS_TOKEN"; // Replace with your access token

// Using OkHttp
OkHttpClient client = new OkHttpClient.Builder().build();
Request request = new Request.Builder()
        .url(apiUrl)
        .addHeader("Authorization", "Bearer " + accessToken)
        .build();

Response response = client.newCall(request).execute();
// Process the API response

Refreshing Access Tokens

Access tokens have a limited lifespan. To ensure continued access to user data, you’ll need to refresh them before they expire. You can use the “refresh token” (obtained during the initial token exchange) to get a new access token without requiring the user to re-authenticate.

// ... (similar to the token exchange code)
String refreshToken = response.getString("refresh_token"); // Store the refresh token

// When the access token expires:
String refreshUrl = "https://oauth2.googleapis.com/token";
String refreshTokenRequest = "grant_type=refresh_token" +
        "&client_id=" + clientId +
        "&client_secret=" + clientSecret +
        "&refresh_token=" + refreshToken;

// Make a POST request to the refresh URL with the refresh token request
// ...

Best Practices

• Store your client ID and secret securely. Avoid hardcoding them directly in your code.
• Implement robust error handling mechanisms to gracefully deal with authentication failures, token expirations, and API errors.
• Respect user privacy by limiting the requested scopes to those strictly necessary for your application’s functionality.
• Consider using a dedicated library to simplify OAuth 2.0 implementation, such as Google Sign-In for Android or iOS.

Conclusion

By embedding a webview and leveraging the Google OAuth 2.0 framework, you can seamlessly integrate Google login functionality into your native applications. This approach offers a secure, user-friendly, and customizable method for accessing Google user data and enhances the overall experience for your app users.