Google has a bunch of apps like Google+, Gmail, Docs, Reader, etc. Internally, these apps must talk to each other securely to query information/data. I am wondering conceptually how Google implements this secured authentication and authorization among their apps internally. Does anyone know about this? 
Google authentication and authorization among their apps
google apps;security;authentication;oauth
They use OAuth2 for authentication and authorization. There are some slight variations on certain services, for example Google Drive. It depends on exactly which service you want to use.