[net] Add support for direct IP connection

- Rewrite the TLS authenticator to ignore DNS/IP verification
- Still as secure as previous implementation

net/client.go

@@ -4,7 +4,11 @@ import (
 	"crypto/rsa"
 	"crypto/tls"
 	"crypto/x509"
+	"errors"
+	"net"
+	"time"
 
+	"golang.org/x/net/context"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
 )
@@ -29,11 +33,89 @@ func Connect(addrPort string, cert *x509.Certificate, key *rsa.PrivateKey, ca *x
 	caCertPool.AddCert(ca)
 
 	// configure transport authentificator
-	ta := credentials.NewTLS(&tls.Config{
-		Certificates: certificates,
-		RootCAs:      caCertPool,
-	})
+	conf := tls.Config{
+		Certificates:       certificates,
+		RootCAs:            caCertPool,
+		InsecureSkipVerify: true, // Don't panic, it's normal and safe. See tlsCreds structure.
+	}
 
 	// let's do the dialing !
-	return grpc.Dial(addrPort, grpc.WithTransportCredentials(ta))
+	return grpc.Dial(
+		addrPort,
+		grpc.WithTransportCredentials(&tlsCreds{config: conf}),
+	)
+}
+
+// tlsCreds reimplements the default grpc TLS authenticator with no hostname verification.
+// It is required because we need to connect to clients with their IP, and there is no IP SANs in our certificates.
+//
+// We need to enable the "InsecureSkipVerify" to perform this, that's why it's important to check the server certificate
+// during the authentication process.
+//
+// See crypto/tls/handshake_client.go and google.golang.org/grpc/credentials/credentials.go
+type tlsCreds struct {
+	config tls.Config
+}
+
+func (c *tlsCreds) Info() credentials.ProtocolInfo {
+	return credentials.ProtocolInfo{
+		SecurityProtocol: "tls",
+		SecurityVersion:  "1.2",
+	}
+}
+
+func (c *tlsCreds) GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error) {
+	return nil, nil
+}
+
+func (c *tlsCreds) RequireTransportSecurity() bool {
+	return true
+}
+
+func (c *tlsCreds) ClientHandshake(addr string, rawConn net.Conn, timeout time.Duration) (_ net.Conn, _ credentials.AuthInfo, err error) {
+	var errChannel chan error
+	if timeout != 0 {
+		errChannel = make(chan error, 2)
+		time.AfterFunc(timeout, func() {
+			errChannel <- errors.New("credentials: Dial timed out")
+		})
+	}
+
+	// Establish a secure connection WITHOUT certificate verification
+	conn := tls.Client(rawConn, &c.config)
+	if timeout == 0 {
+		err = conn.Handshake()
+	} else {
+		go func() { errChannel <- conn.Handshake() }()
+		err = <-errChannel
+	}
+
+	if err != nil { // Error during handshake
+		_ = rawConn.Close()
+		return nil, nil, err
+	}
+
+	// Successful handshake, BUT we have to authentify the server NOW
+	opts := x509.VerifyOptions{
+		Roots:       c.config.RootCAs,
+		CurrentTime: time.Now(),
+	}
+
+	var chains [][]*x509.Certificate
+
+	state := conn.ConnectionState()
+	serverCert := state.PeerCertificates[0]
+	chains, err = serverCert.Verify(opts)
+	state.VerifiedChains = chains
+
+	if err != nil {
+		_ = rawConn.Close()
+		return nil, nil, err
+	}
+
+	return conn, nil, nil
+}
+
+func (c *tlsCreds) ServerHandshake(rawConn net.Conn) (net.Conn, credentials.AuthInfo, error) {
+	return nil, nil, errors.New("Server side handshake not implemented")
 }