JSON Web Token (JWT) Validation in Azure Application Gateway: Secure Your APIs at the Gate
Hello Folks! In a Zero Trust world, identity becomes the control plane and tokens become the gatekeepers. Recently, in an E2E conversation with my colleague Vyshnavi Namani, we dug into a topic every ITPro supporting modern apps should understand: JSON Web Token (JWT) validation, specifically using Azure Application Gateway. In this post we’ll distill that conversation into a technical guide for infrastructure pros who want to secure APIs and backend workloads without rewriting applications. Why IT Pros Should Care About JWT Validation JSON Web Token (JWT) is an open standard token format (RFC 7519) used to represent claims or identity information between two parties. JWTs are issued by an identity provider (Microsoft Entra ID) and attached to API requests in an HTTP Authorization: Bearer <token> header. They are tamper-evident and include a digital signature, so they can be validated cryptographically. JWT validation in Azure Application Gateway means the gateway will check every incoming HTTPS request for a valid JWT before it forwards the traffic to your backend service. Think of it like a bouncer or security guard at the club entrance: if the client doesn’t present a valid “ID” (token), they don’t get in. This first-hop authentication happens at the gateway itself. No extra custom auth code is needed in your APIs. The gateway uses Microsoft Entra ID (Azure AD) as the authority to verify the token’s signature and claims (issuer/tenant, audience, expiry, etc.). By performing token checks at the edge, Application Gateway ensures that only authenticated requests reach your application. If the JWT is missing or invalid, the gateway could deny the request depending on your configuration (e.g. returns HTTP 401 Unauthorized) without disturbing your backend. If the JWT is valid, the gateway can even inject an identity header (x-msft-entra-identity) with the user’s tenant and object ID before passing the call along 9 . This offloads authentication from your app and provides a consistent security gate in front of all your APIs. Key benefits of JWT validation at the gateway: Stronger security at the edge: The gateway checks each token’s signature and key claims, blocking bad tokens before they reach your app. No backend work needed: Since the gateway handles JWT validation, your services don’t need token‑parsing code. Therefore, there is less maintenance and lower CPU use. Stateless and scalable: Every request brings its own token, so there’s no session management. Any gateway instance can validate tokens independently, and Azure handles key rotation for you. Simplified compliance: Centralized JWT policies make it easier to prove only authorized traffic gets through, without each app team building their own checks. Defense in depth: Combine JWT validation with WAF rules to block malicious payloads and unauthorized access. In short, JWT validation gives your Application Gateway the smarts to know who’s knocking at the door, and to only let the right people in. How JWT Validation Works At its core, JWT validation uses a trusted authority (for now it uses Microsoft Entra ID) to issue a token. That token is presented to the Application Gateway, which then validates: The token is legitimate The token was issued by the expected tenant The audience matches the resource you intend to protect If all checks pass, the gateway returns a 200 OK and the request continues to your backend. If anything fails, the gateway returns 403 Forbidden, and your backend never sees the call. You can check code and errors here: JSON Web Token (JWT) validation in Azure Application Gateway (Preview) Setting Up JWT Validation in Azure Application Gateway The steps to configure JWT validation in Azure Application Gateway are documented here: JSON Web Token (JWT) validation in Azure Application Gateway (Preview) Use Cases That Matter to IT Pros Zero Trust Multi-Tenant Workloads Geolocation-Based Access AI Workloads Next Steps Identify APIs or workloads exposed through your gateways. Audit whether they already enforce token validation. Test JWT validation in a dev environment. Integrate the policy into your Zero Trust architecture. Collaborate with your dev teams on standardizing audiences. Resources Azure Application Gateway JWT Validation https://learn.microsoft.com/azure/application-gateway/json-web-token-overview Microsoft Entra ID App Registrations https://learn.microsoft.com/azure/active-directory/develop/quickstart-register-app Azure Application Gateway Documentation https://learn.microsoft.com/azure/application-gateway/overview Azure Zero Trust Guidance https://learn.microsoft.com/security/zero-trust/zero-trust-overview Azure API Management and API Security Best Practices https://learn.microsoft.com/azure/api-management/api-management-key-concepts Microsoft Identity Platform (Tokens, JWT, OAuth2 https://learn.microsoft.com/azure/active-directory/develop/security-tokens Using Curl with JWT Validation Scenarios https://learn.microsoft.com/azure/active-directory/develop/v2-oauth2-client-creds-grant-flow#request-an-access-token Final Thoughts JWT validation in Azure Application Gateway is a powerful addition to your skills for securing cloud applications. It brings identity awareness right into your networking layer, which is a huge win for security and simplicity. If you manage infrastructure and worry about unauthorized access to your APIs, give it a try. It can drastically reduce the “attack surface” by catching invalid requests early. As always, I’d love to hear about your experiences. Have you implemented JWT validation on App Gateway, or do you plan to? Let me know how it goes! Feel free to drop a comment or question. Cheers! Pierre Roman
