Which of the following authentication methods is used to enable a Web browser to provide credentials when making a request during an HTTP transaction?

Anonymous authentication does not require the client to provide any credentials - the server grants access without verifying identity, making it the opposite of the described behavior.

Digest authentication also enables credential submission but uses an MD5 challenge-response mechanism to avoid sending the password in any encoded form, making it a distinct and more secure protocol than what is described.

Integrated Windows authentication uses Kerberos or NTLM tokens negotiated transparently using the user's existing Windows session credentials, rather than having the browser explicitly prompt for and transmit username/password credentials.

Basic authentication, defined in RFC 7617, works by having the server send a WWW-Authenticate header prompting the browser to collect credentials, which are then concatenated, Base64-encoded, and sent in the Authorization header on subsequent requests. It is the simplest and most direct method by which a web browser provides credentials during an HTTP transaction, though it requires HTTPS to be secure.