Allow admins to masquerade as ordinary users

I am the Confluence Admin for our site, and there are often occasions that come up where I wish to masquerade as an ordinary user, to perform actions which will appear as though they originated by that user.

An example might be to change a profile picture (tracked separately in CONF-6112), or to correct spelling errors or formatting issues on a page that another user has authored. Many of our users lack proficiency in web authoring skills, and sometimes discrete "touch ups" or corrections would be highly valuable. In these cases, I do not want the changes to be attributed to an admin user who has performed these changes. It would be best if the changes appear to have been made by the original user.

Many web apps allow an admin to temporarily "become" or otherwise assume the identify of a regular user in order to perform actions that need to be executed as that user. Common examples are content authoring/editing, but this feature is also useful for checking user permissions and application functionality as though one were logged in as that user.