Why Yann LeCun's home page is now password protected?

Just a guess: misconfigured Apache server doesn't handle https:// URL's correctly, and redirects them to HTTP auth. (The server *is* Apache; it *is* a very old version; and the URL you provided *is* an 'http://', which most browsers today will upgrade to 'https://'... which breaks on this website. The server configuration is probably a best practice from several decades ago. If the website worked for you recently, most likely, your browser upgrade broke it).

This is a pretty common regression. If you can find a browser that doesn't force-upgrade TLS, that should be a workaround.

edit to add: wget works! (This is the only one I could get working; lame, I know)

    $ wget https://yann.lecun.com/

    --2022-04-18 ***--  https://yann.lecun.com/
    Resolving yann.lecun.com (yann.lecun.com)... 172.67.171.76, 104.21.29.36, 2606:4700:3036::ac43:ab4c, ...
    Connecting to yann.lecun.com (yann.lecun.com)|172.67.171.76|:443... connected.
    HTTP request sent, awaiting response... 401 Unauthorized
    
    Username/Password Authentication Failed.
    

    $ wget http://yann.lecun.com/

    --2022-04-18 ***--  http://yann.lecun.com/
    Resolving yann.lecun.com (yann.lecun.com)... 172.67.171.76, 104.21.29.36, 2606:4700:3036::ac43:ab4c, ...
    Connecting to yann.lecun.com (yann.lecun.com)|172.67.171.76|:80... connected.
    HTTP request sent, awaiting response... 200 OK
    Length: unspecified [text/html]
    Saving to: ‘index.html’
    
    index.html                [ <=>                   ]  37.65K  --.-KB/s    in 0.001s  
    
    2022-04-18 *** (72.6 MB/s) - ‘index.html’ saved [38556]