curl

1. curl command-line reference

   Options for requests, output, headers and config files.

2. Everything curl overview

   The official book on curl and libcurl.

3. HTTP with curl

   Methods, headers, redirects, versions and HTTP/2 and HTTP/3.

4. POST and uploads

   Form, JSON and multipart bodies, file uploads.

5. Cookies

   Cookie engine, cookie jars and sending cookies.

6. TLS and certificates

   Server certificate verification and CA stores.

7. Proxies

   Using HTTP, HTTPS and SOCKS proxies, proxy authentication and the no-proxy list.

8. Authentication

   Basic, digest, bearer and other auth methods.

9. Other protocols

   FTP, SFTP, SMTP, IMAP, MQTT and others.

10. libcurl tutorial

    Easy and multi interfaces, options and callbacks.

11. Scripting and exit codes

    Exit codes, write-out and use in scripts.

12. Security and vulnerabilities

    Security process and past vulnerabilities.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.