In order for the google oauth login to function, it would need to know where to redirect to, which is why your client ID is required. This is the 32 random looking characters that make up your chrome extension's URL. You can submit an item to the chrome web store. You can use ID that is generated when you load unpacked (this is shown in the chrome://extensions page, as well as being available programmatically at
chrome.runtime.id from within your extension), but that will change once you upload it to the webstore. Once you upload it to the store, you will have an ID automatically generated for you. You also have the choice of
generating a key locally, and then uploading that key to the chrome web store.