diff --git a/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go b/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
new file mode 100644
index 0000000..62ed0f2
--- /dev/null
+++ b/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
@@ -0,0 +1,71 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package envconfig contains grpc settings configured by environment variables.
+package envconfig
+
+import (
+	"os"
+	"strings"
+)
+
+const (
+	prefix              = "GRPC_GO_"
+	retryStr            = prefix + "RETRY"
+	requireHandshakeStr = prefix + "REQUIRE_HANDSHAKE"
+)
+
+// RequireHandshakeSetting describes the settings for handshaking.
+type RequireHandshakeSetting int
+
+const (
+	// RequireHandshakeHybrid (default, deprecated) indicates to not wait for
+	// handshake before considering a connection ready, but wait before
+	// considering successful.
+	RequireHandshakeHybrid RequireHandshakeSetting = iota
+	// RequireHandshakeOn (default after the 1.17 release) indicates to wait
+	// for handshake before considering a connection ready/successful.
+	RequireHandshakeOn
+	// RequireHandshakeOff indicates to not wait for handshake before
+	// considering a connection ready/successful.
+	RequireHandshakeOff
+)
+
+var (
+	// Retry is set if retry is explicitly enabled via "GRPC_GO_RETRY=on".
+	Retry = strings.EqualFold(os.Getenv(retryStr), "on")
+	// RequireHandshake is set based upon the GRPC_GO_REQUIRE_HANDSHAKE
+	// environment variable.
+	//
+	// Will be removed after the 1.18 release.
+	RequireHandshake RequireHandshakeSetting
+)
+
+func init() {
+	switch strings.ToLower(os.Getenv(requireHandshakeStr)) {
+	case "on":
+		fallthrough
+	default:
+		RequireHandshake = RequireHandshakeOn
+	case "off":
+		RequireHandshake = RequireHandshakeOff
+	case "hybrid":
+		// Will be removed after the 1.17 release.
+		RequireHandshake = RequireHandshakeHybrid
+	}
+}