certificates/examples/README.md

Examples

Basic client usage

The basic-client example shows the use of the most of the functioanlity of the ca.Client, those methods works as an SDK for integrating other services with the Certificate Authority (CA).

In basic-client/client.go we first can see the initialization of the client:

client, err := ca.NewClient("https://localhost:9000", ca.WithRootSHA256("84a033e84196f73bd593fad7a63e509e57fd982f02084359c4e8c5c864efc27d"))

The previous code uses the CA address and the root certificate fingerprint. The CA url will be present in the token, and the root fingerprint can be present too if the --root root_ca.crt option is use in the creation of the token. If this is the case is simpler to rely in the token and use just:

client, err := ca.Bootstrap(token)

After the initialization there're examples of all the client methods, they are just a convenient way to use the CA API endpoints. The first method Health returns the status of the CA server, on the first implementation if the server is up it will return just ok.

health, err := client.Health()
// Health is a struct created from the JSON response {"status": "ok"}

The next method Root is used to get and verify the root certificate. We will pass a finger print, it will download the root certificate from the CA and it will make sure that the fingerprint matches. This method uses an insecure HTTP client as it might be used in the initialization of the client, but the response is considered secure because we have compared against the given digest.

root, err := client.Root("84a033e84196f73bd593fad7a63e509e57fd982f02084359c4e8c5c864efc27d")

After Root we have the most important method Sign, this is used to sign a Certificate Signing Request that we provide. To secure this request we use the one-time-token. You can build your own certificate request and add it in the *api.SignRequest, but the ca package contains a method that will create a secure random key, and create the CSR based on the information in the token.

// Create a CSR from token and return the sign request, the private key and an
// error if something failed.
req, pk, err := ca.CreateSignRequest(token)
if err != nil { ... }

// Do the sign request and return the signed certificate
sign, err := client.Sign(req)
if err != nil { ... }

To renew the certificate we can use the Renew method, the certificate renewal relies on a mTLS connection with a previous certificate, so we will need to pass a transport with the previous certificate.

// Get a cancelable context to stop the renewal goroutines and timers.
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
// Create a transport from with the sign response and the private key.
tr, err := client.Transport(ctx, sign, pk)
if err != nil { ... }
// Renew the certificate and get the new ones.
// The return type are equivalent to ones in the Sign method.
renew, err := client.Renew(tr)
if err != nil { ... }

All the previous methods map with one endpoint in the CA API, but the API provides a couple more that are used for creating the tokens. For those we have a couple of methods, one that returns a list of provisioners and one that returns the encrypted key of one provisioner.

// Without options it will return the first 20 provisioners
provisioners, err := client.Provisioners()
// We can also set a limit up to 100
provisioners, err := client.Provisioners(ca.WithProvisionerLimit(100))
// With a pagination cursor
provisioners, err := client.Provisioners(ca.WithProvisionerCursor("1f18c1ecffe54770e9107ce7b39b39735"))
// Or combining both
provisioners, err := client.Provisioners(
    ca.WithProvisionerCursor("1f18c1ecffe54770e9107ce7b39b39735"),
    ca.WithProvisionerLimit(100),
)

// Return the encrypted key of one of the returned provisioners. The key
// returned is an encrypted JWE with the private key used to sign tokens.
key, err := client.ProvisionerKey("DmAtZt2EhmZr_iTJJ387fr4Md2NbzMXGdXQNW1UWPXk")

The example shows also the use of some helper methods used to get configured tls.Config objects that can be injected in servers and clients. These methods, are also configured to auto-renew the certificate once two thirds of the duration of the certificate has passed, approximately.

// Get a cancelable context to stop the renewal goroutines and timers.
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
// Get tls.Config for a server
tlsConfig, err := client.GetServerTLSConfig(ctx, sign, pk)
// Get tls.Config for a client
tlsConfig, err := client.GetClientTLSConfig(ctx, sign, pk)
// Get an http.Transport for a client, this can be used as a http.RoundTripper
// in an http.Client
tr, err := client.Transport(ctx, sign, pk)

To run the example you need to start the certificate authority:

certificates $ bin/step-ca examples/pki/config/ca.json
2018/11/02 18:29:25 Serving HTTPS on :9000 ...

And just run the client.go with a new token:

certificates $ export STEPPATH=examples/pki
certificates $ export STEP_CA_URL=https://localhost:9000
certificates $ go run examples/basic-client/client.go $(step ca new-token client.smallstep.com)

Bootstrap Client & Server

On this example we are going to see the Certificate Authority running, as well as a simple Server using TLS and a simple client doing TLS requests to the server.

The examples directory already contains a sample pki configuration with the password password hardcoded, but you can create your own using step ca init.

These examples show the use of other helper methods, they are simple ways to create TLS configured http.Server and http.Client objects. The methods are BootstrapServer and BootstrapClient and they are used like:

// Get a cancelable context to stop the renewal goroutines and timers.
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
// Create an http.Server
srv, err := ca.BootstrapServer(ctx, token, &http.Server{
    Addr: ":8443",
    Handler: handler,
})
if err != nil {
    panic(err)
}
srv.ListenAndServeTLS("", "")

// Get a cancelable context to stop the renewal goroutines and timers.
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
// Create an http.Client
client, err := ca.BootstrapClient(ctx, token)
if err != nil {
    panic(err)
}
resp, err := client.Get("https://localhost:8443")

To run the example first we will start the certificate authority:

certificates $ bin/step-ca examples/pki/config/ca.json
2018/11/02 18:29:25 Serving HTTPS on :9000 ...

We will start the server and we will type password when step asks for the provisioner password:

certificates $ export STEPPATH=examples/pki
certificates $ export STEP_CA_URL=https://localhost:9000
certificates $ go run examples/bootstrap-server/server.go $(step ca new-token localhost)
✔ Key ID: DmAtZt2EhmZr_iTJJ387fr4Md2NbzMXGdXQNW1UWPXk (mariano@smallstep.com)
Please enter the password to decrypt the provisioner key:
Listening on :8443 ...

We try that using cURL with the system certificates it will return an error:

certificates $ curl https://localhost:8443
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: https://curl.haxx.se/docs/sslcerts.html

curl performs SSL certificate verification by default, using a "bundle"
 of Certificate Authority (CA) public keys (CA certs). If the default
 bundle file isn't adequate, you can specify an alternate file
 using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
 the bundle, the certificate verification probably failed due to a
 problem with the certificate (it might be expired, or the name might
 not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
 the -k (or --insecure) option.
HTTPS-proxy has similar options --proxy-cacert and --proxy-insecure.

But if we use the root certificate it will properly work:

certificates $ curl --cacert examples/pki/secrets/root_ca.crt https://localhost:8443
Hello nobody at 2018-11-03 01:49:25.66912 +0000 UTC!!!

Notice that in the response we see nobody, this is because the server didn't detected a TLS client configuration.

But if we the client with the certificate name Mike we'll see:

certificates $ export STEPPATH=examples/pki
certificates $ export STEP_CA_URL=https://localhost:9000
certificates $ go run examples/bootstrap-client/client.go $(step ca new-token Mike)
✔ Key ID: DmAtZt2EhmZr_iTJJ387fr4Md2NbzMXGdXQNW1UWPXk (mariano@smallstep.com)
Please enter the password to decrypt the provisioner key:
Server responded: Hello Mike at 2018-11-03 01:52:52.678215 +0000 UTC!!!
Server responded: Hello Mike at 2018-11-03 01:52:53.681563 +0000 UTC!!!
Server responded: Hello Mike at 2018-11-03 01:52:54.682787 +0000 UTC!!!
...

Certificate rotation

We can use the bootstrap-server to demonstrate the certificate rotation. We've added second provisioner to to the ca with the name of mike@smallstep.com, this provisioner is configured with a default certificate duration of 2 minutes. If we run the server, and inspect the used certificate, we can verify how it rotates after approximately two thirds of the duration has passed.

certificates $ export STEPPATH=examples/pki
certificates $ export STEP_CA_URL=https://localhost:9000
certificates $ go run examples/bootstrap-server/server.go $(step ca new-token localhost))
✔ Key ID: YYNxZ0rq0WsT2MlqLCWvgme3jszkmt99KjoGEJJwAKs (mike@smallstep.com)
Please enter the password to decrypt the provisioner key:
Listening on :8443 ...

In this specific case, the the rotation will happen after 74-80 seconds have passed, the exact formula is 120-120/3-rand(120/20), where rand will return a number between 0 and 6.

We can use the following command to check the certificate expiration and to make sure the certificate changes after 74-80 seconds.

certificates $ step certificate inspect --insecure https://localhost:8443