Adding reloading of TLS certificates (runatlantis#2656)

* Adding reloading of TLS certificates

* Update server/server.go

Co-authored-by: nitrocode <[email protected]>

* Adding test and test data

* Set minimum tls version

* Adding read header timeout

Co-authored-by: nitrocode <[email protected]>

server/server.go

@@ -17,6 +17,7 @@ package server
 
 import (
 	"context"
+	"crypto/tls"
 	"flag"
 	"fmt"
 	"io"
@@ -112,6 +113,9 @@ type Server struct {
 	ProjectJobsErrorTemplate       templates.TemplateWriter
 	SSLCertFile                    string
 	SSLKeyFile                     string
+	CertLastRefreshTime            time.Time
+	KeyLastRefreshTime             time.Time
+	SSLCert                        *tls.Certificate
 	Drainer                        *events.Drainer
 	WebAuthentication              bool
 	WebUsername                    string
@@ -890,13 +894,15 @@ func (s *Server) Start() error {
 		s.ProjectCmdOutputHandler.Handle()
 	}()
 
-	server := &http.Server{Addr: fmt.Sprintf(":%d", s.Port), Handler: n} // nolint: gosec
+	tlsConfig := &tls.Config{GetCertificate: s.GetSSLCertificate, MinVersion: tls.VersionTLS12}
+
+	server := &http.Server{Addr: fmt.Sprintf(":%d", s.Port), Handler: n, TLSConfig: tlsConfig, ReadHeaderTimeout: 10 * time.Second}
 	go func() {
 		s.Logger.Info("Atlantis started - listening on port %v", s.Port)
 
 		var err error
 		if s.SSLCertFile != "" && s.SSLKeyFile != "" {
-			err = server.ListenAndServeTLS(s.SSLCertFile, s.SSLKeyFile)
+			err = server.ListenAndServeTLS("", "")
 		} else {
 			err = server.ListenAndServe()
 		}
@@ -1012,6 +1018,30 @@ var healthzData = []byte(`{
   "status": "ok"
 }`)
 
+func (s *Server) GetSSLCertificate(*tls.ClientHelloInfo) (*tls.Certificate, error) {
+	certStat, err := os.Stat(s.SSLCertFile)
+	if err != nil {
+		return nil, fmt.Errorf("while getting cert file modification time: %w", err)
+	}
+
+	keyStat, err := os.Stat(s.SSLKeyFile)
+	if err != nil {
+		return nil, fmt.Errorf("while getting key file modification time: %w", err)
+	}
+
+	if s.SSLCert == nil || certStat.ModTime() != s.CertLastRefreshTime || keyStat.ModTime() != s.KeyLastRefreshTime {
+		cert, err := tls.LoadX509KeyPair(s.SSLCertFile, s.SSLKeyFile)
+		if err != nil {
+			return nil, fmt.Errorf("while loading tls cert: %w", err)
+		}
+
+		s.SSLCert = &cert
+		s.CertLastRefreshTime = certStat.ModTime()
+		s.KeyLastRefreshTime = keyStat.ModTime()
+	}
+	return s.SSLCert, nil
+}
+
 // ParseAtlantisURL parses the user-passed atlantis URL to ensure it is valid
 // and we can use it in our templates.
 // It removes any trailing slashes from the path so we can concatenate it

server/server_test.go

@@ -15,6 +15,7 @@ package server_test
 
 import (
 	"bytes"
+	"crypto/tls"
 	"errors"
 	"io"
 	"net/http"
@@ -163,6 +164,30 @@ func BenchmarkHealthz(b *testing.B) {
 	}
 }
 
+func TestGetCertificate(t *testing.T) {
+	s := server.Server{}
+	clientHelloInfo := &tls.ClientHelloInfo{}
+
+	// Initial certificate load
+	s.SSLCertFile = "../testdata/cert.pem"
+	s.SSLKeyFile = "../testdata/key.pem"
+	cert, err := s.GetSSLCertificate(clientHelloInfo)
+	Ok(t, err)
+
+	// Certificate reload
+	s.SSLCertFile = "../testdata/cert2.pem"
+	s.SSLKeyFile = "../testdata/key2.pem"
+	s.CertLastRefreshTime = s.CertLastRefreshTime.Add(-1 * time.Second)
+	s.KeyLastRefreshTime = s.KeyLastRefreshTime.Add(-1 * time.Second)
+	newCert, err := s.GetSSLCertificate(clientHelloInfo)
+
+	Ok(t, err)
+	Assert(
+		t,
+		!bytes.Equal(bytes.Join(cert.Certificate, nil), bytes.Join(newCert.Certificate, nil)),
+		"Certificate expected to rotate")
+}
+
 func TestParseAtlantisURL(t *testing.T) {
 	cases := []struct {
 		In     string

testdata/cert.pem

@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----
+MIIDiDCCAnACCQDOnvpjFkiR7TANBgkqhkiG9w0BAQsFADCBhTELMAkGA1UEBhMC
+YXQxETAPBgNVBAgMCGF0bGFudGlzMREwDwYDVQQHDAhhdGxhbnRpczERMA8GA1UE
+CgwIYXRsYW50aXMxETAPBgNVBAsMCGF0bGFudGlzMREwDwYDVQQDDAhhdGxhbnRp
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+-----END CERTIFICATE-----

testdata/cert2.pem

@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
+MIIDlDCCAnwCCQCGl++WdvHa4jANBgkqhkiG9w0BAQsFADCBizELMAkGA1UEBhMC
+YXQxEjAQBgNVBAgMCWF0bGFudGlzMjESMBAGA1UEBwwJYXRsYW50aXMyMRIwEAYD
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+DYLLTHTfIL4=
+-----END CERTIFICATE-----

testdata/key.pem

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
+MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQDQ+d1Yhu2MBljr
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+bYCXCqkOjIcnONDRDr04jE8c
+-----END PRIVATE KEY-----

testdata/key2.pem

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
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+-----END PRIVATE KEY-----