bip-xchgrate: Note authentication

Author: luke-jr

bip-xchgrate.mediawiki

@@ -25,6 +25,8 @@ Four requests are defined, which are all made by a GET request to a common URI w
 All matching parameters may be specified with multiple comma-separated values, which are to be interpreted as "any of these".
 Each result is always in JSON format, with a line-feed (never a carriage-return) separating multiple results.
 
+Authentication for subscription-based services MAY be supported using standard HTTP authentication.
+
 To be BIP <FIXME> compatible, servers MUST support at least one currency-pair compared to XBT.
 All inquiries for bitcoin amounts MUST be specified in XBT, even if the presentation to the end user is in another unit.
 (FIXME: or should this be satoshis?)