Você pode usar qualquer ferramenta que tenha cabeçalhos HTTP. Exemplo no curl você deve ver o servidor responder com WWW-Authenticate: Basic realm="xxx" se estiver usando autenticação básica.
Se digerir, será parecido com o seguinte.
WWW-Authenticate: Digest realm="[email protected]",
qop="auth,auth-int",
nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",
opaque="5ccc069c403ebaf9f0171e9517f40e41"
Isto é como ver os cabeçalhos em curvas.
$ curl -v http://a.b.c.d/
* About to connect() to a.b.c.d port 80 (#0)
* Trying a.b.c.d...
* Adding handle: conn: 0x7f8e0a008c00
* Adding handle: send: 0
* Adding handle: recv: 0
* Curl_addHandleToPipeline: length: 1
* - Conn 0 (0x7f8e0a008c00) send_pipe: 1, recv_pipe: 0
* Connected to a.b.c.d (a.b.c.d) port 80 (#0)
> GET / HTTP/1.1
> User-Agent: curl/7.30.0
> Host: a.b.c.d
> Accept: */*
>
< HTTP/1.1 401 Authorization Required
< Date: Wed, 05 Nov 2014 07:27:40 GMT
* Server Apache is not blacklisted
< Server: Apache
< WWW-Authenticate: Basic realm="xxx"
< Content-Length: 463
< Content-Type: text/html; charset=iso-8859-1
<
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>401 Authorization Required</title>
</head><body>
<h1>Authorization Required</h1>
<p>This server could not verify that you
are authorized to access the document
requested. Either you supplied the wrong
credentials (e.g., bad password), or your
browser doesn't understand how to supply
the credentials required.</p>
<hr>
<address>Apache Server at a.b.c.d Port 80</address>
</body></html>