This form is only meant for submitting some data to the DeclarativeSecureServlet using the HTTP POST method. Remember that we have allowed only supervisors to access the doPost() of this servlet. Therefore, when you submit the form you will be asked for username/password. And it will work only as per the users specified in tomcat-users.xml (explained in the previous page).
If you enter john/jjj as the username/password, you will not be allowed to access the servlet because john is not configured as a supervisor in tomcat-users.xml. But if you enter bob/bbb, the servlet will be executed because bob is configured as a supervisor.
Also, once you enter a valid username/password (john/jjj or bob/bbb), you'll not be asked for authentication again even if you try to login with a different user name. To change your authentication parameters, you'll have to shutdown all browser windows and access this page again.

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