Following the scheme in a URL, there can be a possible username and password field embedded. The use of this syntax is usually frowned upon these days since you easily leak this information in scripts or otherwise. For example, listing the directory of an FTP server using a given name and password:
curl ftp://user:[email protected]/
The presence of username and password in the URL is completely optional. curl also allows that information to be provided with normal command-line options, outside of the URL.
If you want a non-ASCII letter or maybe a : or @ as part of the username
and/or password, remember to URL encode that letter: write it as %HH where
HH is the hexadecimal byte value. : is %3a and @ is %40.