The code below appears to show the text "HELLO WORLD" just fine in Firefox, IE, Safari, but not in Chrome.
AuthName "HELLO WORLD"
ErrorDocument 401 "Authentication required"
AuthName directive sets the
realm parameter in the corresponding header, something like:
WWW-Authenticate: Basic realm="HELLO WORLD"
I found a Chromium ticket from October 2015 that reports a man in the middle attack related to HTTP authentication: Issue 544244 - HTTP basic auth credentials prompt should make the origin stand out more. During the discussion it was pointed out that text in realm can not be trusted and can be used in phishing attacks to trick users into revealing passwords to third-parties. I'm not a security expert but I understand that a proxy can inject headers —and usually does— thus the issue.
Apparent, the realm was removed form the authentication dialogue as a result of this and changes were eventually ported to Chrome. You can see the Do not show untrustworthy strings in the basic auth dialog code review for further details.