Allow for mTLS connections configured from environment (#237)

* Add clientTLS configurations from environment.
* TLS12 min version

internal/cmd/authenticated/client.go

@@ -1,12 +1,36 @@
 package authenticated
 
 import (
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"net/http"
+	"os"
+
 	"github.com/urfave/cli/v2"
 
 	"github.com/spacelift-io/spacectl/client"
 	"github.com/spacelift-io/spacectl/client/session"
 )
 
+const (
+	// EnvSpaceliftAPIClientTLSCert represents the path to a client certificate for
+	// communicating with the Spacelift API endpoint.
+	EnvSpaceliftAPIClientTLSCert = "SPACELIFT_API_TLS_CERT"
+
+	// EnvSpaceliftAPIClientTLSKey represents the path to a client key for
+	// communicating with the Spacelift API endpoint.
+	EnvSpaceliftAPIClientTLSKey = "SPACELIFT_API_TLS_KEY"
+
+	// EnvSpaceliftAPIClientCA represents the path to a CA bundle for
+	// verifying Spacelift API endpoint.
+	EnvSpaceliftAPIClientCA = "SPACELIFT_API_TLS_CA"
+)
+
+var (
+	errEnvSpaceliftAPIClientCAParse = fmt.Errorf("failed to parse %s", EnvSpaceliftAPIClientCA)
+)
+
 // Client is the authenticated client that can be used by all CLI commands.
 var Client client.Client
 
@@ -15,6 +39,10 @@ var Client client.Client
 func Ensure(*cli.Context) error {
 	ctx, httpClient := session.Defaults()
 
+	if err := configureTLS(httpClient); err != nil {
+		return err
+	}
+
 	session, err := session.New(ctx, httpClient)
 	if err != nil {
 		return err
@@ -24,3 +52,42 @@ func Ensure(*cli.Context) error {
 
 	return nil
 }
+
+// configureTLS configures client TLS from the environment.
+func configureTLS(httpClient *http.Client) error {
+	clientTLS := &tls.Config{
+		MinVersion: tls.VersionTLS12,
+	}
+
+	if caFile, ok := os.LookupEnv(EnvSpaceliftAPIClientCA); ok && caFile != "" {
+		caCert, err := os.ReadFile("cacert")
+		if err != nil {
+			return err
+		}
+
+		caCertPool := x509.NewCertPool()
+		if !caCertPool.AppendCertsFromPEM(caCert) {
+			return errEnvSpaceliftAPIClientCAParse
+		}
+
+		clientTLS.RootCAs = caCertPool
+	}
+
+	keyFile, keyOk := os.LookupEnv(EnvSpaceliftAPIClientTLSKey)
+	certFile, certOk := os.LookupEnv(EnvSpaceliftAPIClientTLSCert)
+
+	if keyOk && keyFile != "" && certOk && certFile != "" {
+		cert, err := tls.LoadX509KeyPair(certFile, keyFile)
+		if err != nil {
+			return err
+		}
+
+		clientTLS.Certificates = []tls.Certificate{cert}
+	}
+
+	httpClient.Transport = &http.Transport{
+		TLSClientConfig: clientTLS,
+	}
+
+	return nil
+}