[galaxy-dev] Galaxy v17.09 impersonation doesn't work

The impersonation feature in Galaxy v17.09 doesn't work as expected. After clicking the person to impersonate, the webpage shows "you have now logged in as xxx, return to home page', where 'xxx' is the name of the person I want to impersonate. So far so good. But after I click home, and check the login information, the login name is still myself. Is there anything I missed in the configuration file? Thanks, Ping