more about passwords and started about proxies

 source code that you write that is using libcurl for transfers. The program

 is outside libcurl and libcurl is outside of the program.

 To get the more details on all options and functions described herein, please

 refer to their respective man pages.

Building

  There are many different ways to build C programs. This chapter will assume

  a unix-style build process. If you use a different build system, you can

  still read this to get general information that may apply to your

  environment as well.

 There are many different ways to build C programs. This chapter will assume a

 unix-style build process. If you use a different build system, you can still

 read this to get general information that may apply to your environment as

 well.

  Compiling the Program

 possible of your code that uses libcurl, operating system name and version,

 compiler name and version etc.

 Getting some in-depth knowledge about the protocols involved is never wrong,

 and if you're trying to funny things, you might very well understand libcurl

 and how to use it better if you study the appropriate RFC documents at least

 briefly.

Upload Data to a Remote Site

        curl_easy_setopt(easyhandle, CURLOPT_PROXYUSERPWD, "myname:thesecret");

  [ more options, setting passsword callback ]

 There's a long time unix "standard" way of storing ftp user names and

 passwords, namely in the $HOME/.netrc file. The file should be made private

 so that only the user may read it (see also the "Security Considerations"

 chapter), as it might contain the password in plain text. libcurl has the

 ability to use this file to figure out what set of user name and password to

 use for a particular host. As an extension to the normal functionality,

 libcurl also supports this file for non-FTP protocols such as HTTP. To make

 curl use this file, use the CURLOPT_NETRC option:

    curl_easy_setopt(easyhandle, CURLOPT_NETRC, TRUE);

 And a very basic example of how such a .netrc file may look like:

    machine myhost.mydomain.com

    login userlogin

    password secretword

 All these examples have been cases where the password has been optional, or

 at least you could leave it out and have libcurl attempt to do its job

 without it. There are times when the password isn't optional, like when

 you're using an SSL private key for secure transfers.

 You can in this situation either pass a password to libcurl to use to unlock

 the private key, or you can let libcurl prompt the user for it. If you prefer

 to ask the user, then you can provide your own callback function that will be

 called when libcurl wants the password. That way, you can control how the

 question will appear to the user.

 To pass the known private key password to libcurl:

    curl_easy_setopt(easyhandle, CURLOPT_SSLKEYPASSWD, "keypassword");

 To make a password callback:

    int enter_passwd(void *ourp, const char *prompt, char *buffer, int len);

    curl_easy_setopt(easyhandle, CURLOPT_PASSWDFUNCTION, enter_passwd);

HTTP POSTing

Proxies

 [ regular http, authorization, ftp => http, SSL, tunneling ]

 What "proxy" means according to Merriam-Webster: "a person authorized to act

 for another" but also "the agency, function, or office of a deputy who acts

 as a substitute for another".

 Proxies are exceedingly common these days. Companies often only offer

 internet access to employees through their HTTP proxies. Network clients or

 user-agents ask the proxy for docuements, the proxy does the actual request

 and then it returns them.

 libcurl has full support for HTTP proxies, so when a given URL is wanted,

 libcurl will ask the proxy for it instead of trying to connect to the actual

 host identified in the URL.

 The fact that the proxy is a HTTP proxy puts certain restrictions on what can

 actually happen. A requested URL that might not be a HTTP URL will be still

 be passed to the HTTP proxy to deliver back to libcurl. This happens

 transparantly, and an application may not need to know. I say "may", because

 at times it is very important to understand that all operations over a HTTP

 proxy is using the HTTP protocol. For example, you can't invoke your own

 custom FTP commands or even proper FTP directory listings.

 To tell libcurl to use a proxy at a given port number:

    curl_easy_setopt(easyhandle, CURLOPT_PROXY, "proxy-host.com:8080");

 Some proxies require user authentication before allowing a request, and you

 pass that information similar to this:

    curl_easy_setopt(easyhandle, CURLOPT_PROXYUSERPWD, "user:password");

 [ environment variables, SSL, tunneling, automatic proxy config (.pac) ]

Security Considerations