moodle/lang/en_utf8/help/authchange.html

<h1>Changing authentication method</h1>

<p>This menu allows you to change the authentication method 
   for this particular user.</p>

<p>Please be aware that this depends very heavily on which 
   authentication methods you have set up for the site, and 
   what settings they are using.</p>

<p>A wrong change here could prevent this person from 
   logging in or even delete their account completely, so 
   please only use it if you know what you are doing.</p>