LTI Customer key

Hello,

I am using the LTI method for the first time, and I am stock ! I hope that someone can help me. I checked the moodle guide https://docs.moodle.org/311/en/Publish_as_LTI_tool and it says "You will also need to give the LTI consumer site a consumer key - this can be anything you want."

I cannot find where I generate the customer key ? As far as i understand, I can make it up myself, but where do I write it down ? 

Thank you so much for your help,