What is a username:password in URI?

Authentication credentials embedded directly in the URI. They identify the user for access to protected resources on the server. Format: scheme://login:password@host:port/path?query#fragment.

Example:

http://admin:password123@example.com/private

Usage is considered insecure because credentials can be compromised (logging, proxies, sniffing). Preferred authentication methods are tokens, cookies, OAuth.