Authentication protocols are essential tools in the digital age, serving as gatekeepers to verify online identities and secure access to protected information and services. They dictate how users (claimants) and authenticators (verifiers) communicate through processes that involve encryption, hashing, and digital signatures to protect sensitive data. Popular protocols include Kerberos, which uses secret-key cryptography for secure communication; Challenge-Response, which involves generating and responding to secure codes; OAuth/OpenID Connect, which facilitates sharing resources and authentication without revealing personal details; SAML, which employs XML for identity exchange and is favored for Single Sign-On (SSO) in enterprise contexts; FIDO2/WebAuthn, which supports passwordless authentication using registered devices or security keys; and TOTP, which generates time-sensitive, one-time passwords for enhanced security. When choosing an authentication protocol, developers should consider factors such as security levels, integration capabilities, scalability, and the desired user authentication experience, often opting for multi-factor authentication for added security. Tools like Descope can simplify the implementation of these protocols by offering a user-friendly platform to integrate secure login features into applications.