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Configuring Mutual Authentication via ApisixTls

In this practice, we will use mTLS to protect our exposed ingress APIs.

To learn more about mTLS, please refer to Mutual authentication

Prerequisites#

  • an available Kubernetes cluster
  • an available APISIX and APISIX Ingress Controller installation

In this guide, we assume that your APISIX is installed in the apisix namespace and ssl is enabled, which is not enabled by default in the Helm Chart. To enable it, you need to set apisix.ssl.enabled=true during installation.

Assuming the SSL port is 9443.

Deploy httpbin service#

We use kennethreitz/httpbin as the service image, See its overview page for details.

Deploy it to the default namespace:

kubectl run httpbin --image kennethreitz/httpbin --port 80
kubectl expose pod httpbin --port 80

Route the traffic#

Since SSL is not configured in ApisixRoute, we can use the config similar to the one in practice Proxy the httpbin service.

# route.yaml
apiVersion: apisix.apache.org/v2
kind: ApisixRoute
metadata:
  name: httpserver-route
spec:
  http:
    - name: httpbin
      match:
        hosts:
          - mtls.httpbin.local
        paths:
          - "/*"
      backends:
        - serviceName: httpbin
          servicePort: 80

Please remember the host field is mtls.httpbin.local. It will be the domain we are going to use.

Test it:

kubectl -n apisix exec -it <APISIX_POD_NAME> -- curl "http://127.0.0.1:9080/ip" -H "Host: mtls.httpbin.local"

It should output:

{
  "origin": "127.0.0.1"
}

Certificates#

Before configuring SSL, we must have certificates. Certificates often authorized by certificate provider, which also known as Certification Authority (CA).

You can use OpenSSL to generate self-signed certificates for testing purposes. Some pre-generated certificates for this guide are here.

  • ca.pem: The root CA.
  • server.pem and server.key: Server certificate used to enable SSL (https). Contains correct subjectAltName matches domain mtls.httpbin.local.
  • user.pem and user.key: Client certificate.

To verify them, use commands below:

openssl verify -CAfile ./ca.pem ./server.pem
openssl verify -CAfile ./ca.pem ./user.pem

Protecting the Route with SSL#

In APISIX Ingress Controller, we use the ApisixTls resource to protect our routes with SSL. This resource requires a secret containing the certificate and private key.

What is the Secret?

The ApisixTls resource needs a Kubernetes secret that contains the SSL certificate and the private key. The cert field of the secret should contain the SSL certificate in PEM format, while the key field should contain the private key in PEM format. These values must be base64-encoded before storing them in the Kubernetes secret.

Here's how to generate the base64 value of the certificate and private key:

base64 -w0 foo.crt # for cert
base64 -w0 foo.key # for private key

Replace the foo.crt and foo.key with the actual names of certificate and private key files, respectively.

Example Keys and Certificates

The examples we use in this guide are available on GitHub.

Creating the Secret

To create the secret, run the following command:

kubectl apply -f ./mtls/server-secret.yaml -n default

This creates a Kubernetes secret with the name server-secret in the default namespace. We will reference this secret in the ApisixTls resource.

Creating the ApisixTls Resource

Next, create the ApisixTls resource to use the certificate and private key from the secret:

# tls.yaml
apiVersion: apisix.apache.org/v2
kind: ApisixTls
metadata:
  name: sample-tls
spec:
  hosts:
    - mtls.httpbin.local
  secret:
    name: server-secret
    namespace: default

The spec field contains the details of the ApisixTls resource, such as the hosts and secret fields. In this example, we are specifying that the SSL certificate should be used for the domain mtls.httpbin.local.

Apply this YAML file to create the ApisixTls resource:

kubectl apply -f tls.yaml -n default

Testing the SSL Configuration

Now since we've configured SSL, we can test it out by sending a request to the protected route. To do this, we'll use the curl command.

kubectl -n apisix exec -it <APISIX_POD_NAME> -- curl --resolve 'mtls.httpbin.local:9443:127.0.0.1' "https://mtls.httpbin.local:9443/ip" -k

Here are some important points to keep in mind:

  • We're using the --resolve parameter to resolve our domain name. This tells curl to resolve mtls.httpbin.local:9443 to 127.0.0.1.
  • We're using the https protocol and the SSL port 9443.
  • We're using the -k parameter to allow insecure connections when using SSL. Since our self-signed certificate is not trusted by default, we need to allow insecure connections. Without the domain mtls.httpbin.local, the request won't succeed.

You can add the -v parameter to log the handshake process.

Now, we configured SSL successfully.

Mutual Authentication#

Like server-secret, we will create a client-ca-secret to store the CA that verify the certificate client presents.

The keys and certificates used in the examples are here.

kubectl apply -f ./mtls/client-ca-secret.yaml -n default

Then, change our ApisixTls and apply it:

# mtls.yaml
apiVersion: apisix.apache.org/v2
kind: ApisixTls
metadata:
  name: sample-tls
spec:
  hosts:
    - mtls.httpbin.local
  secret:
    name: server-secret
    namespace: default
  client:
    caSecret:
      name: client-ca-secret
      namespace: default
    depth: 10

The client field references the secret, depth indicates the max certificate chain length.

Let's try to connect the route without any chanegs:

kubectl -n apisix exec -it <APISIX_POD_NAME> -- curl --resolve 'mtls.httpbin.local:9443:127.0.0.1' "https://mtls.httpbin.local:9443/ip" -k

If everything works properly, it will return a 400 Bad Request.

From APISIX access log, we could find logs like this:

2021/05/27 17:20:54 [error] 43#43: *106132 [lua] init.lua:293: http_access_phase(): client certificate was not present, client: 127.0.0.1, server: _, request: "GET /ip HTTP/2.0", host: "mtls.httpbin.local:9443"
127.0.0.1 - - [27/May/2021:17:20:54 +0000] mtls.httpbin.local:9443 "GET /ip HTTP/2.0" 400 154 0.000 "-" "curl/7.76.1" - - - "http://mtls.httpbin.local:9443"

That means our mutual authentication has been enabled successfully.

Now, we need to transfer our client cert to the APISIX container to verify the mTLS functionality.

The keys and certificates used in the examples are here.

# Transfer client certificate
kubectl -n apisix cp ./user.key <APISIX_POD_NAME>:/tmp/user.key
kubectl -n apisix cp ./user.pem <APISIX_POD_NAME>:/tmp/user.pem

# Test
kubectl -n apisix exec -it <APISIX_POD_NAME> -- curl --resolve 'mtls.httpbin.local:9443:127.0.0.1' "https://mtls.httpbin.local:9443/ip" -k --cert /tmp/user.pem --key /tmp/user.key

Parameter --cert and --key indicates our certificate and key path.

It should output normally:

{
  "origin": "127.0.0.1"
}