Add Google Data technical info from Wiki

docs/technical-reference/google/google-data.md

@@ -0,0 +1,55 @@
+---
+id: google-data
+title: Google Data extension
+sidebar_label: Google Data extension
+---
+
+# Google Data extension (technical)
+
+## Steps to obtain OAuth credentials
+
+:::info
+For the development version of OpenRefine only.  For usage, see [Starting - Create a project by importing data - Google data](manual/starting.md#google-data)
+:::
+
+To obtain data from [Google Drive](https://www.google.com/drive/) or [Google Sheets](https://www.google.com/sheets/about/) for OpenRefine requires OAuth credentials.
+
+## Google API Console 
+For obtaining the OAuth credentials follow these steps:
+
+1. Go to the [Google API Console](https://console.developers.google.com/)
+2. Click on **Create Project**.
+3. Pick a project name such as **My OpenRefine Dev Project**.
+4. Fill the required fields.
+5. Hit **Create** for creating the project. 
+6. Pick **Enable APIs and Services**.
+
+## Enable the services
+* Google Sheets API
+* Google Drive API
+
+## OAuth consent screen pane
+1. Go to the **OAuth consent screen pane**.
+2. As user type, pick **External**. 
+3. Fill the form for the OAuth credentials. 
+4. For the OAuth scopes, pick ../auth/drive/ which will give you write access to your Google Drive.
+5. For the domain (and other URLs), you can pick anything (since the localhost will be allowed anyway). 
+6. Hit **Save** to save the consent screen.
+
+## Credentials pane
+1. Go to the **Credentials pane**.
+2. Create new OAuth credentials, adding as allowed origin `http://127.0.0.1:3333`, and as allowed callback URL: `http://127.0.0.1:3333/extension/gdata/authorized`
+3. Copy your **client id**, **client secret key**
+4. Go back to the **Credentials Pane**, and create a new **API key**. Copy its value.
+5. Backup and save the **client id** and **secret key** in a file __outside__ your git clone of OpenRefine.
+    :::warning
+    Never publish secret keys to public git repos.
+    ::: 
+
+6. Add Java property definitions for your client id and secret key by adding
+
+    ```
+    -Dext.gdata.clientid=<yourid> -Dext.gdata.clientsecret=... -Dext.gdata.apikey=...
+    ```
+
+    to your JVM arguments. This can be done by editing the `refine.ini` file at the root of the code base.

sidebars.js

@@ -59,7 +59,8 @@ module.exports = {
             items: [
             'technical-reference/writing-extensions',
             'technical-reference/migrating-older-extensions',
-            'technical-reference/wikibase/architecture'
+            'technical-reference/wikibase/architecture',
+            'technical-reference/google/google-data',
             ]
         },
         {