Securing and Scaling Hybrid Apps with F5/NGINX (Part 3)

 

In part 2 of our series, I demonstrated how to configure ZT (Zero Trust) use cases centering around authentication with NGINX Plus in hybrid environments. We deployed NGINX Plus as the external LB to route and authenticate users connecting to my Kubernetes applications. 

 

In this article, we explore other areas of the ZT spectrum configurable on the External LB Service, including: 

  • Authorization and Access
  • Encryption mTLS
  • Monitoring/Auditing

ZT Use case #1: Authorization

Many people think that authentication and authorization can be used interchangeably. However, they both mean different things. Authentication involves the process of verifying user identities based on the credentials presented. 

Even though authenticated users are verified by the system, they do not necessarily have the authority to access protected applications. That is where authorization comes into play. Authorization involves the process of verifying the authority of an identity before granting access to application.  

Authorization in the context of OIDC authentication involves retrieving claims from user ID tokens and setting conditions to validate whether the user is authorized to enter the system.  

An authenticated user is granted an ID token from the IdP with specific user information through JWT claims. The configuration of these claims is typically set from the IdP. Revisiting the OIDC auth use case configured in the previous section, we can retrieve the ID tokens of authenticated users from the NGINX key-value store.   

$ curl -i http://localhost:8010/api/9/http/keyvals/oidc_acess_tokens

Then we can view the decoded value of the ID token using jwt.io. Below is an example of decoded payload data from the ID token. 

{
"exp": 1716219261, 
"iat": 1716219201, 
"admin": true, 
"name": "Micash", 
"zone_info": "America/Los_Angeles" 
"jti": "9f8ff4bd-4857-4e12-9634-e5876f786f98", 
"iss": "http://idp.f5lab.com:8080/auth/realms/master", 
"aud": "account", "typ": "Bearer",
"azp": "appworld2024", 
"nonce": "gMNK3tu06j6tp5-jGa3aRhkj4F0P-Z3e04UfcFeqbes"
}

NGINX Plus has access to these claims as embedded variables. They are accessed by prefixing $jwt_claim_ to the desired field (for example, $jwt_claim_admin for the admin claim). We can easily set conditions on these claims and block unauthorized users before they even reach the back-end applications. 

Going back to our frontend.conf file in the previous part of our series. We can set $jwt_flag variable to 0 or 1 based on the value of the admin JWT claim. We then use the jwt_claim_require directive to validate the ID token. ID tokens with admin claims set to false will be rejected.  

map $jwt_claim_admin $jwt_status { 
    "true" 1;
    default 0; 
} 
server { 
    include conf.d/openid_connect.server_conf; # Authorization code flow and Relying Party processing 
    error_log /var/log/nginx/error.log debug; # Reduce severity level as required 
    listen [::]:443 ssl ipv6only=on;
    listen 443 ssl;  
    server_name example.work.gd; 
    ssl_certificate /etc/ssl/nginx/default.crt; # self-signed for example only
    ssl_certificate_key /etc/ssl/nginx/default.key;

    location / { 
       # This site is protected with OpenID Connect
       auth_jwt "" token=$session_jwt;
       error_page 401 = @do_oidc_flow;
       auth_jwt_key_request /_jwks_uri; # Enable when using URL
       auth_jwt_require $jwt_status;
       proxy_pass https://cluster1-https; # The backend site/app
    }
}

Note: Authorization with NGINX Plus is not restricted to only JWT tokens. You can technically set conditions on a variety of attributes, such as:

  • Session cookies
  • HTTP headers
  • Source/Destination IP addresses

ZT use case #2: Mutual TLS Authentication (mTLS)

When it comes to ZT,  mTLS is one of the mainstream use cases falling under the Zero Trust umbrella. For example, enterprises are using Service Mesh technologies to stay compliant with ZT standards. This is because Service Mesh technologies aim to secure service to service communication using mTLS.  

In many ways, mTLS is similar to the OIDC use case we implemented in the previous section. Only here, we are leveraging digital certificates to encrypt and authenticate traffic. This underlying framework is defined by PKI (Public Key Infrastructure). 

To explain this framework in simple terms we can refer to a simple example; the driver's license you carry in your wallet. Your driver’s license can be used to validate your identity, the same way digital certificates can be used to validate the identity of applications. Similarly, only the state can issue valid driver's licenses, the same way only Certificate Authorities (CAs) can issue valid certificates to applications. It is also important that only the state can issue valid certificates. Therefore, every CA must have a private secure key to sign and issue valid certificates. 

Configuring mTLS with NGINX can be broken down in two parts:  

  • Ingress mTLS; Securing SSL client traffic and validating client certificates against a trusted CA.
  • Egress mTLS; securing SSL upstream traffic and offloading authentication of TLS material to a trusted HTTPS back-end server.

Ingress mTLS

You can configure ingress mTLS on the NLK deployment by simply referencing the trusted certificate authority adding the ssl_client_certificate directive in the server context. This will configure NGINX to validate client certificates with the referenced CA.

Note: If you do not have a CA, you can create one using OpenSSL or Cloudflare PKI and TLS toolkits  

server {
   listen 443 ssl;
   status_zone https://cafe.example.com;
   server_name cafe.example.com;
   ssl_certificate /etc/ssl/nginx/default.crt;
   ssl_certificate_key /etc/ssl/nginx/default.key;
   ssl_client_certificate /etc/ssl/ca.crt;
}

Egress mTLS

Egress mTLS is a slight alternative to ingress mTLS where NGINX verifies certificates of upstream applications rather than certificates originating from clients. This feature can be enabled by adding the proxy_ssl_trusted_certificate directive to the server context. You can reference the same trusted CA we used for verification when configuring ingress mTLS or reference a different CA. 

In addition to verifying server certificates, NGINX as a reverse-proxy can pass over certs/keys and offload verification to HTTPS upstream applications. This can be done by adding the proxy_ssl_certificate and proxy_ssl_certificate_key directives in the server context. 

server {
   listen 443 ssl;
   status_zone https://cafe.example.com;
   server_name cafe.example.com;
   ssl_certificate /etc/ssl/nginx/default.crt;
   ssl_certificate_key /etc/ssl/nginx/default.key;

   #Ingress mTLS
   ssl_client_certificate /etc/ssl/ca.crt;

   #Egress mTLS
   proxy_ssl_certificate /etc/nginx/secrets/default-egress.crt;
   proxy_ssl_certificate_key /etc/nginx/secrets/default-egress.key;
   proxy_ssl_trusted_certificate /etc/nginx/secrets/default-egress-ca.crt;
}

ZT use case #3: Secure Assertion Markup Language (SAML)

SAML (Security Assertion Markup Language) is an alternative SSO solution to OIDC. Many organizations may choose between SAML and OIDC depending on requirements and IdPs they currently run in production. SAML requires a SP (Service Provider) to exchange XML messages via HTTP POST binding to a SAML IdP.  Once exchanges between the SP and IdP are successful, the user will have session access to the protected backed applications with one set of user credentials.  

In this section, we will configure NGINX Plus as the SP and enable SAML with the IdP.  This will be like how we configured NGINX Plus as the relying party in an OIDC authorization code flow (See ZT Use case #1).  

Setting up the IdP

The one prerequisite is setting up your IdP. In our example, we will set up the Microsoft Entra ID on Azure. You can use the SAML IdP of your choosing. Once the SAML application is created in your IdP, you can access the SSO fields necessary to link your SP (NGINX Plus) to your IdP (Microsoft Entra ID).

 

You will need to edit the basic SAML configuration by clicking on the pencil icon next to Edit in Basic SAML Configuration, as seen in the figure above.

Add the following values and click Save: 

  • Identifier (Entity ID) -- https://fourth.run.place
  • Reply URL (Assertion Consumer Service URL) -- https://fourth.run.place/saml/acs
  • Sign on URL: https://fourth.run.place
  • Logout URL (Optional): https://fourth.run.place/saml/sls

Finally download the Certificate (Raw) from Microsoft Entra ID and save it to your NGINX Plus instance. This certificate is used to verify signed SAML assertions received from the IdP. Once the certificate is saved on the NGINX Plus instance, extract the public key from the downloaded certificate and convert it to SPKI format. We will use this certificate later when we configure NGINX Plus in the next section.

$ openssl x509 -in demo-nginx.der -outform DER -out demo-nginx.der
$ openssl x509 -inform DER -in demo-nginx.der -pubkey -noout > demo-nginx.spki

Configuring NGINX Plus as the SAML Service Provider

After the IdP is setup, we can configure NGINX Plus as the SP to exchange and validate XML messages with the IdP.  Once logged into the NGINX Plus instance, simply clone the nginx SAML GitHub repo.

$ git clone https://github.com/nginxinc/nginx-saml.git && cd nginx-saml

Copy the config files into the /etc/nginx/conf.d directory.

$ cp frontend.conf saml_sp.js saml_sp.server_conf saml_sp_configuration.conf /etc/nginx/conf.d/

Notice that by default, frontend.conf listens on port 8010 with clear text http. You can merge kube_lb.conf into frontend.conf to enable TLS termination and update the upstream context with application endpoints you wish to protect with SAML.

Finally we will need to edit the saml_sp_configuration.conf file and update variables in the map context based on the parameters of your SP and IdP: 

  • $saml_sp_entity_id; https://fourth.run.place
  • $saml_sp_acs_url; https://fourth.run.place/saml/acs
  • $saml_sp_sign_authn; false
  • $saml_sp_want_signed_response; false
  • $saml_sp_want_signed_assertion; true
  • $saml_sp_want_encrypted_assertion; false
  • $saml_idp_entity_id; Unique identifier that identifies the IdP to the SP. This field is retrieved from your IdP
  • $saml_idp_sso_url; This is the login URL and is also retrieved from the IdP
  • $saml_idp_verification_certificate; Variable referencing the certificate downloaded from the previous section when setting up the IdP. This certificate will verify signed assertions received from the IdP. Use the full directory (/etc/nginx/conf.d/demo-nginx.spki)
  • $saml_sp_slo_url; https://fourth.run.place/saml/sls
  • $saml_idp_slo_url; This is the logout URL retrieved from the IdP
  • $saml_sp_want_signed_slo; true

The remaining variables defined in saml_sp_configuration.conf can be left unchanged, unless there is a specific requirement for enabling them. Once the variables are set appropriately, we can reload NGINX Plus. 

$ nginx -s reload

Testing

Now we will verify the SAML flow. open your browser and enter https://fourth.run.place in the address bar. This should redirect me to the IDP login page.

 

Once you login with your credentials, I should be granted access to my protected application

ZT use case #4: Monitoring/Auditing

NGINX logs/metrics can be exported to a variety of 3rd party providers including: Splunk, Prometheus/Grafana, cloud providers (AWS CloudWatch and Azure Monitor Logs), Datadog, ELK stack, and more.

You can monitor NGINX metrics and logs natively with NGINX Instance Manager or NGINX SaaS. The NGINX Plus API provides me a lot of flexibility by exporting metrics to any third-party tool that accepts JSON. For example, you can export NGINX Plus API metrics to our native real-time dashboard from part 1. 

native real-time dashboard from part 1

Whichever tool I chose, monitoring/auditing my data generated from my IT systems is key to understanding and optimizing my applications.

Conclusion

Cloud providers offer a convenient way to expose Kubernetes Services to the internet. Simply create Kubernetes Service of type: LoadBalancer and external users connect to your services via public entry point. However, cloud load balancers do nothing more than basic TCP/HTTP load balancing. You can configure NGINX Plus with many Zero Trust capabilities as you scale out your environment to multiple clusters in different regions, which is what we will cover in the next part of our series. 

 

Updated Jun 18, 2024
Version 2.0
application delivery
cloud
devops
kubernetes
Multicloud Networking
NGINX
NGINX Plus
zero trust

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