User Representation allows a logged-in user to represent another user. The term to represent means that a logged-in user can gain access to another user's application as his/her representative. The representee does not have to be logged in explicitly, and the representer may act on his/her behalf.
It is critical that this feature is configured correctly, as otherwise, it could cause serious security flaws.
In particular, it is highly recommended to restrict usage of the feature to a trusted internal network as shown on User representation system design.