`url-get-authentication'. Their meaning depends on the current
implementation - this function is well and truly coupled.
-url-get-authentication' calls `url-ntlm-auth' once when checking
+`url-get-authentication' calls `url-ntlm-auth' once when checking
what authentication schemes are supported (PROMPT and ARGS are
nil), and then twice for every stage of the handshake: the first
time PROMPT is nil, the second, t; ARGS contains the server