4 Help: Proxy user and password
6 Specify the user name and password to use for proxy authentication.
8 If you use a Windows SSPI-enabled curl binary and do either Negotiate or NTLM
9 authentication then you can tell curl to select the user name and password
10 from your environment by specifying a single colon with this option: "-U :".
12 If this option is used several times, the last one will be used.