Add backwards compat support for API env vars (#7135)

Several env vars got renamed in
https://github.com/hashicorp/vault/pull/6306. This re-adds support for
those.

Indirectly addresses
https://github.com/hashicorp/consul-template/pull/1233 although they
should still update to the new values.

api/client_test.go

@@ -2,12 +2,13 @@ package api
 
 import (
 	"bytes"
-	"github.com/hashicorp/vault/sdk/helper/consts"
 	"io"
 	"net/http"
 	"os"
 	"strings"
 	"testing"
+
+	"github.com/hashicorp/vault/sdk/helper/consts"
 )
 
 func init() {
@@ -196,6 +197,22 @@ func TestClientEnvSettings(t *testing.T) {
 	}
 }
 
+func TestClientDeprecatedEnvSettings(t *testing.T) {
+	oldInsecure := os.Getenv(EnvVaultInsecure)
+	os.Setenv(EnvVaultInsecure, "true")
+	defer os.Setenv(EnvVaultInsecure, oldInsecure)
+
+	config := DefaultConfig()
+	if err := config.ReadEnvironment(); err != nil {
+		t.Fatalf("error reading environment: %v", err)
+	}
+
+	tlsConfig := config.HttpClient.Transport.(*http.Transport).TLSClientConfig
+	if tlsConfig.InsecureSkipVerify != true {
+		t.Fatalf("bad: %v", tlsConfig.InsecureSkipVerify)
+	}
+}
+
 func TestClientEnvNamespace(t *testing.T) {
 	var seenNamespace string
 	handler := func(w http.ResponseWriter, req *http.Request) {