Zscaler oneAPI utilizes the OAuth 2.0 authorization framework for authentication, specifically employing the Client Credentials grant type. In this flow, an API client uses its pre-configured Client ID and Client Secret to request an access token from the Zscaler authentication server. This bearer token must then be presented in the Authorization header for all subsequent API calls. OpenID Connect (OIDC) is an identity layer built on top of OAuth 2.0. Among the choices provided, OIDC is the most accurate representation of the modern, token-based authentication mechanism that Zscaler has implemented for its oneAPI platform.

B. Transport Layer Security (TLS) is a protocol for encrypting data in transit. While API calls must be made over a TLS-secured channel (HTTPS), TLS itself is not the method for authenticating the client to the API service.

C. Security Assertion Markup Language (SAML) is a standard primarily designed for web-based Single Sign-On (SSO) for human users, not for the server-to-server or programmatic authentication required by APIs.

D. System for Cross-domain Identity Management (SCIM) is a protocol for automating user provisioning (e.g., creating, updating, and deleting user accounts), not for authenticating API requests.

1. Zscaler Help Portal

"About oneAPI": This document states

"oneAPI uses the OAuth 2.0 authorization framework with the Client Credentials grant type for authentication. To authenticate to oneAPI

you must first create an API key in the Zscaler Cloud & Branch Connector Admin Portal. The API key consists of a Client ID and a Client Secret. You then use the Client ID and Client Secret to obtain a bearer token from the Zscaler authentication server." (Section: Authentication)

2. Zscaler Help Portal

"Getting Started with oneAPI": This guide provides a step-by-step walkthrough of the authentication process

detailing how to "Obtain a Bearer Token" by making a POST request to the /oauth/token endpoint using the clientcredentials grant type. (Section: Step 2: Obtain a Bearer Token)