Implement CSR validation

This commit adds CSR validation and generation of a baseline requirements
compatible request token instead of a UUID.

Logging has been configured to use timestamps.

handlers/registry.go

@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"crypto/x509"
 	"encoding/pem"
 	"errors"
@@ -11,7 +12,6 @@ import (
 	"os/exec"
 	"time"
 
-	"github.com/google/uuid"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -29,20 +29,58 @@ func NewSigningRequestRegistry(caCertificates []*x509.Certificate) *SigningReque
 	}
 }
 
+type SigningRequestAttributes struct {
+	CommonName   string
+	CSRBytes     []byte
+	RequestToken string
+}
+
 func (registry *SigningRequestRegistry) AddSigningRequest(request *requestData) (string, error) {
-	requestUuid, err := uuid.NewRandom()
+	requestToken, csrBytes, err := validateCsr(request.Csr)
 	if err != nil {
 		return "", err
 	}
+	requestAttributes := &SigningRequestAttributes{
+		CommonName:   request.CommonName,
+		CSRBytes:     csrBytes,
+		RequestToken: requestToken,
+	}
 	go func() {
 		responseChannel := make(chan *responseData, 1)
-		registry.requests[requestUuid.String()] = responseChannel
-		registry.signCertificate(responseChannel, request)
+		registry.requests[requestToken] = responseChannel
+		registry.signCertificate(responseChannel, requestAttributes)
 	}()
-	return requestUuid.String(), nil
+	return requestToken, nil
 }
 
-func (registry *SigningRequestRegistry) signCertificate(channel chan *responseData, request *requestData) {
+func validateCsr(csr string) (string, []byte, error) {
+	csrBlock, _ := pem.Decode([]byte(csr))
+	if csrBlock == nil {
+		return "", nil, errors.New("request data did not contain valid PEM data")
+	}
+	if csrBlock.Type != "CERTIFICATE REQUEST" {
+		return "", nil, fmt.Errorf("request is not valid, type in PEM data is %s", csrBlock.Type)
+	}
+	var err error
+	var csrContent *x509.CertificateRequest
+	csrContent, err = x509.ParseCertificateRequest(csrBlock.Bytes)
+	if err != nil {
+		return "", nil, err
+	}
+	if err = csrContent.CheckSignature(); err != nil {
+		log.Errorf("invalid CSR signature %v", err)
+		return "", nil, err
+	}
+
+	// generate request token as defined in CAB Baseline Requirements 1.7.3 Request Token definition
+	requestToken := fmt.Sprintf(
+		"%s%x", time.Now().UTC().Format("200601021504"), sha256.Sum256(csrContent.Raw),
+	)
+	log.Debugf("generated request token %s", requestToken)
+	return requestToken, csrContent.Raw, nil
+}
+
+func (registry *SigningRequestRegistry) signCertificate(channel chan *responseData, request *SigningRequestAttributes) {
 	responseData, err := registry.sign(request)
 	if err != nil {
 		log.Error(err)
@@ -52,21 +90,26 @@ func (registry *SigningRequestRegistry) signCertificate(channel chan *responseDa
 	channel <- responseData
 }
 
-func (registry *SigningRequestRegistry) sign(request *requestData) (response *responseData, err error) {
-	log.Debugf("received CSR for %s:\n\n%s", request.CommonName, request.Csr)
+func (registry *SigningRequestRegistry) sign(request *SigningRequestAttributes) (*responseData, error) {
+	log.Infof("handling signing request %s", request.RequestToken)
 	subjectDN := fmt.Sprintf("/CN=%s", request.CommonName)
+
+	var err error
 	var csrFile *os.File
 	if csrFile, err = ioutil.TempFile("", "*.csr.pem"); err != nil {
 		log.Errorf("could not open temporary file: %s", err)
-		return
+		return nil, err
 	}
-	if _, err = csrFile.Write([]byte(request.Csr)); err != nil {
+	if err = pem.Encode(csrFile, &pem.Block{
+		Type:  "CERTIFICATE REQUEST",
+		Bytes: request.CSRBytes,
+	}); err != nil {
 		log.Errorf("could not write CSR to file: %s", err)
-		return
+		return nil, err
 	}
 	if err = csrFile.Close(); err != nil {
 		log.Errorf("could not close CSR file: %s", err)
-		return
+		return nil, err
 	}
 	defer func(file *os.File) {
 		err = os.Remove(file.Name())
@@ -81,7 +124,7 @@ func (registry *SigningRequestRegistry) sign(request *requestData) (response *re
 	opensslCommand := exec.Command(
 		"openssl", "ca", "-config", "ca.cnf",
 		"-policy", "policy_match", "-extensions", "client_ext",
-		"-batch", "-subj", subjectDN, "-utf8", "-rand_serial", "-in", "in.pem")
+		"-batch", "-subj", subjectDN, "-utf8", "-rand_serial", "-in", csrFile.Name())
 	var out, cmdErr bytes.Buffer
 	opensslCommand.Stdout = &out
 	opensslCommand.Stderr = &cmdErr
@@ -89,32 +132,32 @@ func (registry *SigningRequestRegistry) sign(request *requestData) (response *re
 	if err != nil {
 		log.Error(err)
 		log.Error(cmdErr.String())
-		return
+		return nil, err
 	}
 
 	var block *pem.Block
 	if block, _ = pem.Decode(out.Bytes()); block == nil {
 		err = fmt.Errorf("could not decode pem")
-		return
+		return nil, err
 	}
 	var certificate *x509.Certificate
 	if certificate, err = x509.ParseCertificate(block.Bytes); err != nil {
-		return
+		return nil, err
 	}
 
 	var caChain []string
 	if caChain, err = registry.getCAChain(certificate); err != nil {
-		return
+		return nil, err
 	}
 
-	response = &responseData{
+	response := &responseData{
 		Certificate: string(pem.EncodeToMemory(&pem.Block{
 			Type:  "CERTIFICATE",
 			Bytes: certificate.Raw,
 		})),
 		CAChain: caChain,
 	}
-	return
+	return response, nil
 }
 
 func (registry *SigningRequestRegistry) GetResponseChannel(requestUuid string) (chan *responseData, error) {

handlers/signing.go

@@ -53,7 +53,7 @@ func (h *CertificateSigningHandler) ServeHTTP(w http.ResponseWriter, r *http.Req
 
 type requestData struct {
 	Csr        string `json:"csr"`
-	CommonName string `json:"commonName"`
+	CommonName string `json:"common_name"`
 }
 
 type responseData struct {