Just noticed what the issue on the login form is: the login URL without ?page is used, and it goes to an error page (since you don't have the clean URLs).
Here's a workaround (not with functions.php though)
1. On your current login page, right click login field and click inspect element.
2. Check my attached screenshot below. You will see a highlighted "form action" with your login URL. (example URL from screenshot: https://www.wondercms.com/demo/loginURL
3. Change it to https://www.wondercms.com/demo/?page=loginURL
(replace with your own domain add the ?page= parameter)
4. You can close the browser inspector and then enter your password and login successfully.
5. While being logged in, create a new page (example: mySecretLoginURL), which will be used as your new login URL.
6. Paste the below code on your mySecretLoginURL page. Replace the URL in the code below with same URL as step 3 above.
Code: Select all
<form action="https://www.wondercms.com/demo/?page=loginURL" method="post"><div class="input-group"><input type="password" class="form-control" id="password" name="password"><span class="input-group-btn"><button type="submit" class="btn btn-info">Login</button></span></div></form>
7. Make sure you hide this page from the menu (Settings-General) (note: it does not hide it from search engines like the original login URL does)
8. You can log out and visit the ?page=mySecretLoginURL to test out how your new/second login page works.
Edit: fixed typo in form action URL.