Hey, this is step by step, hope this helps you ...
Step 1: Go to the Google Developer Console and create a new application

Step 2: enable google plus api


You can see the activation of the api on the Enable API tab, which is located next to the API Library , which is visible in the second image.
Step 3: go to the credentials in the API and auth tab, then select the credentials option
select the type of authentication required
then you can see the configuration confirmation screen to customize the page with the information you want to provide.

Step 4: Select the web application option at the top and enter the required URL

and finally click create
as soon as you do that. You can see ... client id and client secret key ...

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