password-protected pages break

### Impacted plugin

Super Cache

### Quick summary

WordPress pages that are password protected never succeed to show the content.

### Steps to reproduce

In WordPress a page can be password protected.

The page first shows only a password prompt. When that is given, the actual content of the page appears.

This seems to be broken in WP Super Cache. Submitting the password produces only the password prompt again.

Including the URL of the page in the Rejected URL Strings setting fails to fix it. Even deleting the cache fails to fix it.

An example page is https://aacny.org/wordpress/tsl/. The correct password is TSL.

### Site owner impact

Fewer than 20% of the total website/platform users

### Severity

Moderate

### What other impact(s) does this issue have?

No revenue impact

### If a workaround is available, please outline it here.

None that I know of.

### Platform (Simple and/or Atomic)

Simple

Start by reproducing the issue on the example WordPress page using the stated password, then inspect the Super Cache handling for password-protected pages and rejected URL strings. Done means submitting the password reveals the page content instead of returning the password prompt again, while caching remains functional.

Written by the indexing model from the issue text.