Web services: app checks to token.php cause errors in log

1. Disable web services in your server (set 'enablewebservices' config checkbox off, it's under 'Advanced features' in the admin settings).
2. In your browser, visit the URL /login/token.php?appsitecheck=1
   • EXPECTED: An error should be reported in JSON format, 'Web services must be enabled in Advanced features'
3. Enable web services in your server (set the checkbox on),
4. In your browser, visit the URL /login/token.php?appsitecheck=1
   • EXPECTED: You should see a JSON response with appsitecheck "ok".

Only if you have a version of the mobile app/Moodle Desktop with MOBILE-3556 applied, then you can also do this test:

1. Start the mobile app with no data (the easiest way to do this is using Moodle Desktop, open developer tools, then go to the Application tab and clear storage, then press F5 to reload).
2. Click 'I'm a learner' and type or paste in the URL to your site, then select it to proceed to the login screen. (You do not need to actually log in but you should see the login/password fields.)
   • EXPECTED: You get to the login screen without error.
3. Examine the web server error log for your Moodle server, looking for errors at the time that you did the login.
   • EXPECTED: There are no errors at that time. Specifically, there is no error like the following: 'Default exception handler: A required parameter (username) was missing'