This ranking is based on the security of how credentials are handled and the underlying cryptographic protocols.

• Basic authentication is the weakest because it sends the username and password over the network in a plaintext-equivalent form (Base64 encoding), offering no confidentiality.
• Digest authentication is an improvement, using a challenge-response protocol that avoids sending the password in the clear. However, it typically relies on the MD5 hashing algorithm, which is now considered cryptographically weak and vulnerable.
• Integrated Windows Authentication (IWA) is strong as it leverages secure, ticket-based protocols like Kerberos or the NTLMv2 challenge-response mechanism. These protocols are designed to prove a user's identity without transmitting passwords across the network.
• Client Certificate authentication is the strongest. It uses Public Key Infrastructure (PKI) for mutual authentication between the client and server. The client must possess a private key corresponding to its public certificate, providing a much higher level of identity assurance than password-based systems.

Internet Engineering Task Force (IETF). (2015). RFC 7617: The 'Basic' HTTP Authentication Scheme. Section 4: Security Considerations. This section explicitly states, "In the absence of a secure channel, the 'Basic' authentication scheme transmits credentials in the clear."

Internet Engineering Task Force (IETF). (2015). RFC 7616: HTTP Digest Access Authentication. Section 5: Security Considerations. This document discusses the advantages of Digest over Basic but notes its vulnerabilities, including the weakness of the default MD5 algorithm.

Stallings, W., & Brown, L. (2018). Computer Security: Principles and Practice (4th ed.). Pearson. In Chapter 20.3, "HTTPS," the text discusses client certificates as a strong authentication mechanism as part of TLS mutual authentication.

Microsoft Documentation. (2021). Integrated Windows Authentication. Microsoft Learn. This document details how IWA uses Kerberos and NTLM, stating, "With Integrated Windows authentication, user credentials aren't sent to the server." This inherent design makes it stronger than schemes that transmit credentials or their weak derivatives.