code: def confirm_email(self, token):
          
          expired, invalid, user = \
              self.security_utils_service.confirm_email_token_status(token)
          if not user or invalid:
              invalid = True
              self.flash(
                  _('flask_unchained.bundles.security:flash.invalid_confirmation_token'),
                  category='error')
  
          already_confirmed = user is not None and user.confirmed_at is not None
          if expired and not already_confirmed:
              self.security_service.send_email_confirmation_instructions(user)
              self.flash(_('flask_unchained.bundles.security:flash.confirmation_expired',
                           email=user.email,
                           within=app.config.SECURITY_CONFIRM_EMAIL_WITHIN),
                         category='error')
  
          if invalid or (expired and not already_confirmed):
              return self.redirect('SECURITY_CONFIRM_ERROR_REDIRECT_ENDPOINT',
                                   'security_controller.send_confirmation_email')
  
          if self.security_service.confirm_user(user):
              self.after_this_request(self._commit)
              self.flash(_('flask_unchained.bundles.security:flash.email_confirmed'),
                         category='success')
          else:
              self.flash(_('flask_unchained.bundles.security:flash.already_confirmed'),
                         category='info')
  
          if user != current_user:
              self.security_service.logout_user()
              self.security_service.login_user(user)
  
          return self.redirect('SECURITY_POST_CONFIRM_REDIRECT_ENDPOINT',
                               'SECURITY_POST_LOGIN_REDIRECT_ENDPOINT')
docs: View function to confirm a user's token from the confirmation email send to them.
          Supports html and json requests.