Google oAuth Angular service
Do you think there will be security issues if I put this code I made onto the client side?


Yes. You should not expose your Google API key to other users - it should be hidden away on your server. You should expose an end point on an API server that will run the Google OAuth actions. This is known as the three-legged or server-side OAuth flow.

The security reasons mainly come down to the fact that if someone knows your API key then they can masquerade as you. This is usually solved by a shared secret (or just a private key), but the Google OAuth flow doesn't appear to provide this.

You can see here for Google's own resource on best practises for API keys.