How to obtain a refresh token with oauth2 for Google Contacts API 3.0?

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To obtain a refresh token with OAuth2 for Google Contacts API 3.0, follow these steps:

1. Create a Google Cloud Platform project and enable the Contacts API. This can be done by following the steps outlined in the Google Contacts API documentation.

2. Create a new OAuth2 client ID in the Google Cloud Platform console. You will need to specify the redirect URI for your application.

3. Use the OAuth2 authorization flow to obtain an access token. This can be done using one of the Google-supported OAuth2 libraries or manually with a standard HTTP request.

4. Once you have an access token, you can use it to make API requests to the Google Contacts API.

5. When your access token expires, you can use the refresh token to obtain a new access token. This can be done using the same OAuth2 library or with a standard HTTP request.

6. Store the refresh token securely, as it enables long-term access to the user's Google account.