MCP Client Authentication

When running the server over HTTP (sse or streamable-http), authentication controls who is allowed to connect to the server. This is independent from the Zscaler API credentials (which control how the server authenticates to Zscaler APIs).

For stdio transport, MCP client auth is not applicable — the operating system's process isolation provides security.

Auto-detection

For HTTP transports the server auto-enables authentication when any of these environment variables is present:

• ZSCALER_MCP_AUTH_API_KEY → api-key mode
• ZSCALER_MCP_AUTH_JWKS_URI → jwt mode
• ZSCALER_CLIENT_ID + auth-mode flag → zscaler mode

Or set explicitly:

ZSCALER_MCP_AUTH_ENABLED=true
ZSCALER_MCP_AUTH_MODE=jwt

Four supported modes

Mode	Client sends	Best for
api-key	Authorization: Bearer <key>	Quick setup, internal environments, dev
jwt	Authorization: Bearer <jwt>	Enterprise SSO, multi-tenant (Auth0, Okta, Entra ID, Keycloak, Cognito, PingOne, Google)
zscaler	Authorization: Basic base64(client_id:client_secret)	Environments already using Zscaler OneAPI credentials
OIDCProxy (programmatic)	OAuth 2.1 flow with DCR	Library consumers, full MCP-spec OAuth, any OIDC provider

api-key mode

ZSCALER_MCP_AUTH_MODE=api-key
ZSCALER_MCP_AUTH_API_KEY=your-shared-secret

Generate a key:

zscaler-mcp --generate-auth-token

Client uses:

Authorization: Bearer your-shared-secret

jwt mode

Validate JWTs issued by your enterprise IdP using its JWKS endpoint:

ZSCALER_MCP_AUTH_MODE=jwt
ZSCALER_MCP_AUTH_JWKS_URI=https://your-idp.example.com/.well-known/jwks.json
ZSCALER_MCP_AUTH_ISSUER=https://your-idp.example.com/
ZSCALER_MCP_AUTH_AUDIENCE=zscaler-mcp-server

Tokens are validated locally — no per-request call to the IdP. Compatible with any OIDC provider that exposes a JWKS endpoint.

See Microsoft Entra ID setup for a step-by-step example.

zscaler mode

Reuse your Zscaler OneAPI credentials for MCP client authentication:

ZSCALER_MCP_AUTH_MODE=zscaler
# Uses ZSCALER_CLIENT_ID + ZSCALER_CLIENT_SECRET already in your .env

Client sends Basic auth:

Authorization: Basic base64(client_id:client_secret)

The server validates against Zscaler's /oauth2/v1/token endpoint and caches the result for the token's lifetime (~1 hour). This is the default mode used by all GCP and Azure deployment integrations.

OAuth 2.1 with DCR (programmatic)

For full MCP-spec OAuth 2.1 with Dynamic Client Registration, use the auth= parameter when embedding the server as a library. The OIDCProxy stub works with any OIDC provider:

from fastmcp.server.auth.providers.oidc import OIDCProxy
from zscaler_mcp import ZscalerMCPServer

oidc = OIDCProxy(
    issuer="https://your-idp.example.com/",
    audience="zscaler-mcp-server",
    # ... provider-specific config
)

server = ZscalerMCPServer(auth=oidc)
server.run(transport="streamable-http")

This bypasses the env-var middleware entirely.

Network-level controls

In addition to client authentication, the server enforces:

• TLS by default — non-localhost deployments must provide certificates (or set ZSCALER_MCP_ALLOW_HTTP=true)
• Host header validation — ZSCALER_MCP_ALLOWED_HOSTS allowlist
• Source IP ACL — ZSCALER_MCP_ALLOWED_SOURCE_IPS allowlist

See TLS & hardening for details.