In this example, the foo.html page is being requested from the www.example.com web server.

curl https://www.example.com/foo.html

Let's say access to this page require basic authentication (username/password). The -u or --user option can be used to include a username and password in the request.

curl --user john.doe:itsasecret https://www.example.com/foo.html

Special Characters

Be aware that if the username or password contains special characters, such as an exclamation point . . . 

curl --user john.doe:itsa!secret https://www.example.com/foo.html

Something like this will be returned.

-bash: !s: event not found

Special characters will need to be escaped, like like.

curl --user john.doe:itsa\!secret https://www.example.com/foo.html