Prefer "Impersonate" login function

This is a function I've seen in a different product that was incredibly useful. Bascially, it allows a developer to authenticate a user session on behalf of X user without having access to X user's password. The api takes three parameters: admin user name, admin user password, and the user name of user X, the user to be impersonated in this session. This allows applications outside Confluence ... portlets, for example ... to perform Confluence tasks on the balf of users without having assess to a user's Confluence password and without worrying that the external application will show content or perform functions that the user does not have permissions for.