The authority component

The authority has a designated prefix: the special delimiter of two consecutive forward slash (//) characters, whose presence indicates that characters that follow should be parsed according to the specification for a URL authority. This prefix is optionally followed by access credentials, or user information, which transmits an optional user ID and/or password to the destination host. These values, if included, will always be separated from one another with a colon (:) as a delimiter, and will be separated from the rest of the authority component with an at sign (@) delimiter.

Whether access credentials are included as part of the authority or not, it will always include a host domain. This always follows either the double forward slash (//) prefix, or, in the event of access credentials, the (@) delimiter. The host domain specifies the physical address of the hardware hosting the resource being located. It can be specified as either a registered domain name, or the underlying IP address for the hardware.

Finally, an authority might specify a listening port on the host. This is delimited from the host domain name or IP address by the colon (:) character, and indicates the only ports on the hardware to which requests for the specified resource should be sent.