The only interesting fact is that Google App engine is Platform-as-a-service (as opposed to Amazon EC2 which is Infrastructure-as-a-service).
Here is a deployment diagram and the various components involved. As shown in the diagram, the identities of the user rests in a LDAP or Active Directory inside the enterprise domain usually protected by a firewall. Apps 1 and 2 are deployed inside the domain of the enterprise while App 3 is deployed on Google App Engine (different domain) . The user may access the resource either when he is inside the enterprise, or when outside from a kiosk, etc.
In all cases, the user should be authenticated using credentials of the enterprise. Google App Engine credentials may be used for single sign on but it is not mandatory.
The system administrator should be able to define access management rules for the user based on the user's identity inside the enterprise.
Here is how RSA Access Manager can be configured to access the authorization-rules server to determine access to users. Firstly, we would require an Access Manager agent at the Google App Engine server. App Engine Java version provides Server filters that intercept requests before they access the actual resource. Here is how the work flow proceeds.
- User accesses a resource on App engine. He is not logged into Google or on the enterprise.
- The filter intercepts the request and does a URLFetch to the Access Manager Authorization-rules engine, deployed inside the firewall.
- This communication is secured by using Google Secure Data Connector. This could also have been secured using mutual SSL if URL Fetch would allow it.
- The server sees that the there is no cookie set in the request and replies to the agent that authentication needs to be performed.
- The agent sends back a redirect response that throws the user to the authentication page hosted inside the enterprise domain.
- User authenticated at this page. If the user is inside the enterprise, he could be authenticated using NTML, etc.
- If credentials are correct, a cookie for the enterprise domain is set.
- The user is then redirected to the resource page, carrying a message from the server to set a cookie for the Google domain.
- The agent sets the cookie and again redirects to the resource page.
- Since the resource is still protected by the filter, the filter kicks in again and does a URL Fetch to the server to see if the user is allowed.
- The server sees the cookie that is sent in this request and decides on if this user is allowed access or not.
- The agent sees the reply from the server and redirects or blocks the user, depending on the response.
Hence, using this simple filter, you can protect your applications that have moved to the external cloud just like resources are managed inside the enterprise. Adequate measures to secure the communication between the agent in App engine and the Authorization server ensure that this deployment is secure like it was when inside the firewall.