Identity federation combines user trust from an external identity provider with your internal services, without storing credentials locally. In cloud networks, this allows controlled, temporary access to resources. In a Virtual Private Cloud (VPC), a private subnet keeps those resources isolated from the public internet. A proxy inside that subnet becomes the controlled conduit, mediating traffic, enforcing policy, and reducing attack surface.
A correct deployment starts with establishing secure peering between your VPC and the identity provider’s authorization endpoints. This connection runs through a proxy configured within the private subnet. The proxy is hardened, stripped of unnecessary services, and locked to known CIDR ranges. TLS termination should occur at the proxy, with mutual TLS for sensitive workloads.
The service in the private subnet does not initiate outbound internet connections. Instead, the proxy handles all outbound requests needed for identity federation token exchange. Using short-lived tokens or SAML assertions, the proxy validates identities, caches claims securely in memory, and injects headers into downstream requests. It must log every transaction while never leaking secrets into persistent storage.
Security groups should whitelist only the proxy’s IP for inbound access to the service. Network ACLs can provide an extra layer by denying all traffic by default. Deploy the proxy in redundant availability zones to maintain uptime if a zone fails. Regularly rotate signing keys and verify metadata from the identity provider to prevent stale or compromised trust relationships.