Follow this steps to generate your client id. The google client-id is required to the login button.
Access this page to start your google credentials configuration.
Click on the button Configure Project and in the window set a name of your project. Select the option YES on the terms of service and click on NEXT.
Specify the product name that will be show for the users during the login proccess. After chosed the name click on NEXT.
Now you have to choose a kind of client id you want to create. Select the option Web Server
After chosed the option Web Server the window will ask you to set the matrix callback url. This is an important step. You have to talk with your IT department to indicate the correct domain link of your service. In this example we are configuring for local environment, so we inputed the value localhost http://localhost:8080/auth/google/callback for the local tests. In your case the value will be like this: http://mydomain.com/auth/google/callback
Now you have the valid client Id and Client Secret. You will use this values in the next step.
You have to copy Client ID and Client Secret and set the environent variable like this sample:
GOOGLE_CLIENT_ID=00000000-xxxxxxxxxxxxx.apps.googleusercontent.com
GOOGLE_SECRET=g4xxxxxxxxxxxxxxxxxxss
GOOGLE_CALLBACK_URL=http://localhost:8080/auth/google/callback