Password protected sites producing an error (and more problems)

[Zodiac1978]

I think 401 should be ignored too, like 405:
https://github.com/pluginkollektiv/spcl/blob/develop/inc/class-spcl.php#L230

People could want to link on password protected sites which need authorization.
See also: https://core.trac.wordpress.org/ticket/36638#comment:5

Maybe just rejecting 404 and 410 as suggested here:
https://core.trac.wordpress.org/ticket/36638#comment:7

On the other hand the whole check is not very reliable at all:
https://core.trac.wordpress.org/ticket/36638#comment:28

Linkedin pages are returning 999 as status code for example.
Medium seems to reject Requests from WordPress with a 403.
https://core.trac.wordpress.org/ticket/36638#comment:32

And more reasons to skip the whole thing altogether:
https://core.trac.wordpress.org/ticket/36638#comment:46

[patrickrobrecht]

I think that the current check should be ok as dealing with all the mentioned cases may hide real errors as well. Maybe we could add a hint that there might be false positives.

[patrickrobrecht]

Another idea would be to add specific URLs (those which require login, specific user rights or are password protected) to an ignore list (you would get the error once and could click on "Ignore" and afterwards the error is hidden). Linkedin and Medium could be in the ignore list by default due to their rejection of WordPress requests.

This way we avoid to hide actual errors.