internal/credentials: fix a bug and add one more helper function

internal/credentials/spiffe.go

@@ -25,6 +25,7 @@ package credentials
 
 import (
 	"crypto/tls"
+	"crypto/x509"
 	"net/url"
 
 	"google.golang.org/grpc/grpclog"
@@ -38,8 +39,17 @@ func SPIFFEIDFromState(state tls.ConnectionState) *url.URL {
 	if len(state.PeerCertificates) == 0 || len(state.PeerCertificates[0].URIs) == 0 {
 		return nil
 	}
+	return SPIFFEIDFromCert(state.PeerCertificates[0])
+}
+
+// SPIFFEIDFromCert parses the SPIFFE ID from x509.Certificate. If the SPIFFE
+// ID format is invalid, return nil with warning.
+func SPIFFEIDFromCert(cert *x509.Certificate) *url.URL {
+	if cert == nil {
+		return nil
+	}
 	var spiffeID *url.URL
-	for _, uri := range state.PeerCertificates[0].URIs {
+	for _, uri := range cert.URIs {
 		if uri == nil || uri.Scheme != "spiffe" || uri.Opaque != "" || (uri.User != nil && uri.User.Username() != "") {
 			continue
 		}
@@ -48,7 +58,7 @@ func SPIFFEIDFromState(state tls.ConnectionState) *url.URL {
 			logger.Warning("invalid SPIFFE ID: total ID length larger than 2048 bytes")
 			return nil
 		}
-		if len(uri.Host) == 0 || len(uri.RawPath) == 0 || len(uri.Path) == 0 {
+		if len(uri.Host) == 0 || len(uri.Path) == 0 {
 			logger.Warning("invalid SPIFFE ID: domain or workload ID is empty")
 			return nil
 		}
@@ -57,7 +67,7 @@ func SPIFFEIDFromState(state tls.ConnectionState) *url.URL {
 			return nil
 		}
 		// A valid SPIFFE certificate can only have exactly one URI SAN field.
-		if len(state.PeerCertificates[0].URIs) > 1 {
+		if len(cert.URIs) > 1 {
 			logger.Warning("invalid SPIFFE ID: multiple URI SANs")
 			return nil
 		}

internal/credentials/spiffe_test.go

@@ -21,10 +21,13 @@ package credentials
 import (
 	"crypto/tls"
 	"crypto/x509"
+	"encoding/pem"
+	"io/ioutil"
 	"net/url"
 	"testing"
 
 	"google.golang.org/grpc/internal/grpctest"
+	"google.golang.org/grpc/testdata"
 )
 
 type s struct {
@@ -178,3 +181,25 @@ func (s) TestSPIFFEIDFromState(t *testing.T) {
 		})
 	}
 }
+
+func (s) TestSPIFFEIDFromCert(t *testing.T) {
+	data, err := ioutil.ReadFile(testdata.Path("x509/spiffe_cert.pem"))
+	if err != nil {
+		t.Fatalf("Failed to load the test credentials: %v", err)
+	}
+	block, rest := pem.Decode(data)
+	if len(rest) != 0 {
+		t.Fatalf("Failed to parse the certificate: invalid format")
+	}
+	cert, err := x509.ParseCertificate(block.Bytes)
+	if err != nil {
+		t.Fatalf("Failed to load the test credentials: %v", err)
+	}
+	uri := SPIFFEIDFromCert(cert)
+	if uri == nil {
+		t.Fatalf("SPIFFE ID is nil")
+	}
+	if uri.String() != "spiffe://foo.bar.com/client/workload/1" {
+		t.Fatalf("SPIFFE ID not expected, got %s, want %s", uri.String(), "spiffe://foo.bar.com/client/workload/1")
+	}
+}

testdata/x509/create.sh

@@ -100,5 +100,16 @@ openssl x509 -req           \
   -extensions test_client
 openssl verify -verbose -CAfile client_ca_cert.pem  client2_cert.pem
 
+# Generate a cert with SPIFFE ID.
+openssl req -x509                                                         \
+  -newkey rsa:4096                                                        \
+  -keyout spiffe_key.pem                                                  \
+  -out spiffe_cert.pem                                                    \
+  -nodes                                                                  \
+  -days 3650                                                              \
+  -subj /C=US/ST=CA/L=SVL/O=gRPC/CN=test-client1/                         \
+  -addext "subjectAltName = URI:spiffe://foo.bar.com/client/workload/1"
+openssl verify -verbose -CAfile client_ca_cert.pem  client1_spiffe_cert.pem
+
 # Cleanup the CSRs.
-rm *_csr.pem
+rm *_csr.pem

testdata/x509/spiffe_cert.pem

@@ -0,0 +1,33 @@
+-----BEGIN CERTIFICATE-----
+MIIFsjCCA5qgAwIBAgIUPxiyjwxoDyMeRvl4g9TSdvLlCA0wDQYJKoZIhvcNAQEL
+BQAwTjELMAkGA1UEBhMCVVMxCzAJBgNVBAgMAkNBMQwwCgYDVQQHDANTVkwxDTAL
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+p+z97N7TvWfgE1HOmYDfsbaHjPFZKg==
+-----END CERTIFICATE-----

testdata/x509/spiffe_key.pem

@@ -0,0 +1,52 @@
+-----BEGIN PRIVATE KEY-----
+MIIJQwIBADANBgkqhkiG9w0BAQEFAASCCS0wggkpAgEAAoICAQCV84YR/EV55qfF
+ynHhQvWEZW5hUI9q0DeD5kG5CarrkOj11rZuQIBZ7X23CJbeoVbrvbYLghsPYJzx
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+Xgln2zbN6APAb+dGDdv27dz4YlasU4s=
+-----END PRIVATE KEY-----