In order to provide customer verification using the Envato Login button, you need to do the steps below:
1- Go to the "Settings" page, click on the "Envato Integration" tab and copy the "Confirmation URL" to your clipboard:

2- Go to https://build.envato.com/ and login to your Envato account, then go to "My Apps".
3- Then, click on the "Register a new app" button:

4- In the opening page, the checkboxes for "Required Permissions" should be checked as shown below:

5- Then, paste your copied confirmation URL and click on the "Register App" button:

6- Copy your "secret application key" and store it somewhere to use it later:

7- You should be able to see you app registered like shown below. Copy your OAuth Client ID and store it somewhere as well (to be used in the next step):

8- Go back to your Settings page "Envato Integration" tab and enter the client ID and secret key you have stored earlier to the related fields and click on the "Save" button:

9- All done! your Envato Integration for customer verification is complete.