add unit testing and documentation

security/advancedtls/advancedtls.go

@@ -556,6 +556,11 @@ func (c *advancedTLSCreds) OverrideServerName(serverNameOverride string) error {
 //  1. does not have a good support on root cert reloading.
 //  2. will ignore basic certificate check when setting InsecureSkipVerify
 //     to true.
+//
+// peerVerifiedChains(output param): verified chain of certs from leaf to the
+// trust cert that the peer trusts.
+//  1. For server it is, client certs + Root ca that the server trusts
+//  2. For client it is, server certs + Root ca that the client trusts
 func buildVerifyFunc(c *advancedTLSCreds,
 	serverName string,
 	rawConn net.Conn,
@@ -637,7 +642,9 @@ func buildVerifyFunc(c *advancedTLSCreds,
 				VerifiedChains: chains,
 				Leaf:           leafCert,
 			})
-			return err
+			if err != nil {
+				return err
+			}
 		}
 		*peerVerifiedChains = chains
 		return nil

security/advancedtls/advancedtls_test.go

@@ -19,6 +19,7 @@
 package advancedtls
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
 	"crypto/x509"
@@ -896,6 +897,76 @@ func (s) TestClientServerHandshake(t *testing.T) {
 				t.Fatalf("c.ClientHandshake(_, %v, _) = %v, want %v.", lisAddr,
 					clientAuthInfo, serverAuthInfo)
 			}
+			serverVerifiedChains := serverAuthInfo.(credentials.TLSInfo).State.VerifiedChains
+			if test.serverMutualTLS && !test.serverExpectError {
+				if len(serverVerifiedChains) == 0 {
+					t.Fatalf("server verified chains is empty")
+				}
+				var clientCert *tls.Certificate
+				if len(test.clientCert) > 0 {
+					clientCert = &test.clientCert[0]
+				} else if test.clientGetCert != nil {
+					cert, _ := test.clientGetCert(&tls.CertificateRequestInfo{})
+					clientCert = cert
+				} else if test.clientIdentityProvider != nil {
+					km, _ := test.clientIdentityProvider.KeyMaterial(nil)
+					clientCert = &km.Certs[0]
+				}
+				if !bytes.Equal((*serverVerifiedChains[0][0]).Raw, clientCert.Certificate[0]) {
+					t.Fatal("server verifiedChains leaf cert doesn't match client cert")
+				}
+
+				var serverRoot *x509.CertPool
+				if test.serverRoot != nil {
+					serverRoot = test.serverRoot
+				} else if test.serverGetRoot != nil {
+					result, _ := test.serverGetRoot(&GetRootCAsParams{})
+					serverRoot = result.TrustCerts
+				} else if test.serverRootProvider != nil {
+					km, _ := test.serverRootProvider.KeyMaterial(nil)
+					serverRoot = km.Roots
+				}
+				serverVerifiedChainsCp := x509.NewCertPool()
+				serverVerifiedChainsCp.AddCert(serverVerifiedChains[0][len(serverVerifiedChains[0])-1])
+				if !serverVerifiedChainsCp.Equal(serverRoot) {
+					t.Fatalf("server verified chain hierarchy doesn't match")
+				}
+			}
+			clientVerifiedChains := clientAuthInfo.(credentials.TLSInfo).State.VerifiedChains
+			if test.serverMutualTLS && !test.clientExpectHandshakeError {
+				if len(clientVerifiedChains) == 0 {
+					t.Fatalf("client verified chains is empty")
+				}
+				var serverCert *tls.Certificate
+				if len(test.serverCert) > 0 {
+					serverCert = &test.serverCert[0]
+				} else if test.serverGetCert != nil {
+					cert, _ := test.serverGetCert(&tls.ClientHelloInfo{})
+					serverCert = cert[0]
+				} else if test.serverIdentityProvider != nil {
+					km, _ := test.serverIdentityProvider.KeyMaterial(nil)
+					serverCert = &km.Certs[0]
+				}
+				if !bytes.Equal((*clientVerifiedChains[0][0]).Raw, serverCert.Certificate[0]) {
+					t.Fatal("client verifiedChains leaf cert doesn't match server cert")
+				}
+
+				var clientRoot *x509.CertPool
+				if test.clientRoot != nil {
+					clientRoot = test.clientRoot
+				} else if test.clientGetRoot != nil {
+					result, _ := test.clientGetRoot(&GetRootCAsParams{})
+					clientRoot = result.TrustCerts
+				} else if test.clientRootProvider != nil {
+					km, _ := test.clientRootProvider.KeyMaterial(nil)
+					clientRoot = km.Roots
+				}
+				clientVerifiedChainsCp := x509.NewCertPool()
+				clientVerifiedChainsCp.AddCert(clientVerifiedChains[0][len(clientVerifiedChains[0])-1])
+				if !clientVerifiedChainsCp.Equal(clientRoot) {
+					t.Fatalf("client verified chain hierarchy doesn't match")
+				}
+			}
 		})
 	}
 }