From Network Perimeter to Identity Perimeter

Identity-Aware Proxy (IAP) is a GCP service that controls access to applications by verifying user identity and context before allowing requests through. It acts as a gatekeeper that checks who you are, what device you're using, and where you're connecting from on every single request.

Traditional VPNs operate on an all-or-nothing model where authenticated users gain broad network access. Once connected, a compromised credential grants unrestricted access across your entire infrastructure. Identity-Aware Proxy (IAP) fundamentally shifts this model by treating every request as a zero-trust event. Each HTTP request is independently authenticated against Google Identity, Workspace accounts, or external identity providers through SAML and OIDC protocols. This contains the impact of credential compromise, with observed breach damage reductions of approximately 80% compared to traditional VPN architectures.

The security model evaluates not just user identity but contextual signals including device security posture, geographic location, and IP reputation. Access decisions happen at the request level rather than the session level, meaning a user's context change mid-session can immediately affect their access rights.

IAP Architecture as Reverse Proxy

IAP functions as a reverse proxy layer that sits between your users and backend applications. When deployed on GCP load balancers or App Engine, it terminates TLS connections and performs authentication before traffic reaches your application tier.

Artifact: IAP Request Flow

User Request → Load Balancer → IAP Layer → Application
                                    ↓
                            Identity Verification
                            Context Evaluation
                            JWT Injection

After successful authentication, IAP injects verified identity headers into requests: "X-Goog-Authenticated-User-Email" contains the user's email, while "X-Goog-IAP-JWT-Assertion" provides a signed JWT token your application can independently verify. This eliminates the need for applications to implement OAuth flows, session management, or token validation, allowing backend services to trust the identity information implicitly.

Implementation: 15-Minute Internal Tool Protection

Enabling IAP for internal dashboards or admin tools requires minimal configuration. Navigate to your GCP load balancer settings, enable IAP, and configure the OAuth consent screen with your organization's branding. Access control happens through standard IAM bindings where you assign "roles/iap.httpsResourceAccessor" to users or groups. This role can be scoped to specific backend services, allowing granular control like giving engineering team access to monitoring dashboards while restricting financial tools to finance team members.

For App Engine applications, IAP integrates directly without requiring load balancer configuration. The same IAM role controls access at the service or version level, making it practical to protect development environments differently from production.

Cost Economics and Applied Insight

IAP pricing starts at zero cost for the first 1 million requests per project monthly, then charges $0.011 per thousand requests beyond that threshold. A typical internal tool serving 100 employees with moderate usage falls well within the free tier. Enterprise VPN solutions typically cost $500 to $5,000 monthly for licensing, infrastructure, and maintenance, making IAP economically advantageous even before considering reduced operational overhead.

The decision point becomes clear: if you're protecting web applications or SSH access to VMs, IAP provides stronger security guarantees at lower cost. Traditional VPNs remain relevant for scenarios requiring full network protocol support or legacy applications that cannot operate behind HTTP proxies.