If an OFBiz user (whose session has not expired) stays within the processing domain of a single OFBiz webapp, they will not need to log in more than once. But, because of the nature of TCP/IP sessions and servlet container behavior, users moving between OFBiz webapps may be prompted to log in once for each OFBiz webapp they wish to access. Since any single OFBiz instance may support an unlimited number of webapps, certain users such as administrators may need to log in many times in the course of performing a single administrative task.
To help mitigate this situation, OFBiz provides a handy mechanism called the "External Login Key". This feature enables logged in users to move between OFBiz web applications requiring authentication without having to log in more than one time.