3.2.2. Server-based Naming Authority

URL schemes that involve the direct use of an IP-based protocol to a
specified server on the Internet use a common syntax for the server
component of the URI's scheme-specific data:

"@:
"
where may consist of a user name and, optionally, scheme-
specific information about how to gain authorization to access the
server. The parts "@" and ":" may be omitted.

server = [ [ userinfo "@" ] hostport ]

The user information, if present, is followed by a commercial at-sign
"@".

userinfo = *( unreserved | escaped |
";" | ":" | "&" | "=" | "+" | "$" | "," )

Some URL schemes use the format "user:password" in the userinfo
field. This practice is NOT RECOMMENDED, because the passing of
authentication information in clear text (such as URI) has proven to
be a security risk in almost every case where it has been used.