I am working on Google API like chat, contacts and so on...
I am stuck on developer_key
as mentioned in gdata doc.
You can get this at https://code.goog
In the old console layout :
In the new cloud console layout :
In case of both procedures, you find your client ID and client secret at the same page. If you're using a different client ID and client secret, replace it with the ones you find here.
During my first experiments today, I've succesfully used the "Key for server apps" as a developer key for connecting with the "contacts", "userinfo" and "analytics" API. I did this using the PHP client.
Wading through the Google API docs certainly is a pain in the @$$... I hope this info will be useful to anyone.