code: protected void doExecuteCommand() {
          if(!ValkyrieRepository.getInstance().getApplicationConfig().applicationSecurityManager().isSecuritySupported()) {
              return ;
          }
          CompositeDialogPage tabbedPage = new TabbedDialogPage( "loginForm" );
  
          final LoginForm loginForm = createLoginForm();
  
          tabbedPage.addForm( loginForm );
  
          if( getDefaultUserName() != null ) {
              loginForm.setUserName( getDefaultUserName() );
          }
  
          dialog = new TitledPageApplicationDialog( tabbedPage ) {
              protected boolean onFinish() {
                  loginForm.commit();
                  Authentication authentication = loginForm.getAuthentication();
  
                  // Hand this token to the security manager to actually attempt the login
                  ApplicationSecurityManager sm = getApplicationConfig().applicationSecurityManager();
                  try {
                      sm.doLogin( authentication );
                      postLogin();
                      return true;
                  } finally {
                      if( isClearPasswordOnFailure() ) {
                          loginForm.setPassword("");
                      }
                      loginForm.requestFocusInWindow();
                  }
              }
  
              protected void onCancel() {
                  super.onCancel(); // Close the dialog
  
                  // Now exit if configured
                  if( isCloseOnCancel() ) {
                      ApplicationSecurityManager sm = getApplicationConfig().applicationSecurityManager();
                      Authentication authentication = sm.getAuthentication();
                      if( authentication == null ) {
                          LoginCommand.this.logger.info( "User canceled login; close the application." );
                          getApplicationConfig().application().close();
                      }
                  }
              }
  
              protected ActionCommand getCallingCommand() {
                  return LoginCommand.this;
              }
  
              protected void onAboutToShow() {
                  loginForm.requestFocusInWindow();
              }
          };
          dialog.setDisplayFinishSuccessMessage( displaySuccessMessage );
          dialog.showDialog();
      }
docs: Execute the login command. Display the dialog and attempt authentication.