feat(internal): add some feature flags for new auth libs

internal/settings.go

@@ -9,13 +9,19 @@ import (
 	"crypto/tls"
 	"errors"
 	"net/http"
+	"os"
+	"strconv"
 
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	"google.golang.org/api/internal/impersonate"
 	"google.golang.org/grpc"
 )
 
+const (
+	newAuthLibEnVar = "GOOGLE_API_GO_EXPERIMENTAL_USE_NEW_AUTH_LIB"
+)
+
 // DialSettings holds information needed to establish a connection with a
 // Google API service.
 type DialSettings struct {
@@ -47,6 +53,7 @@ type DialSettings struct {
 	ImpersonationConfig           *impersonate.Config
 	EnableDirectPath              bool
 	EnableDirectPathXds           bool
+	EnableNewAuthLibrary          bool
 	AllowNonDefaultServiceAccount bool
 
 	// Google API system parameters. For more information please read:
@@ -77,6 +84,16 @@ func (ds *DialSettings) HasCustomAudience() bool {
 	return len(ds.Audiences) > 0
 }
 
+func (ds *DialSettings) IsNewAuthLibraryEnabled() bool {
+	if ds.EnableNewAuthLibrary {
+		return true
+	}
+	if b, err := strconv.ParseBool(os.Getenv(newAuthLibEnVar)); err == nil {
+		return b
+	}
+	return false
+}
+
 // Validate reports an error if ds is invalid.
 func (ds *DialSettings) Validate() error {
 	if ds.SkipValidation {

option/internaloption/internaloption.go

@@ -150,6 +150,19 @@ func (w *withCreds) Apply(o *internal.DialSettings) {
 	o.InternalCredentials = (*google.Credentials)(w)
 }
 
+// EnableNewAuthLibrary returns a ClientOption that specifies if libraries in this
+// module to delegate auth to our new library. This option will be removed in
+// the future once all clients have been moved to the new auth layer.
+func EnableNewAuthLibrary() option.ClientOption {
+	return enableNewAuthLibrary(true)
+}
+
+type enableNewAuthLibrary bool
+
+func (w enableNewAuthLibrary) Apply(o *internal.DialSettings) {
+	o.EnableNewAuthLibrary = bool(w)
+}
+
 // EmbeddableAdapter is a no-op option.ClientOption that allow libraries to
 // create their own client options by embedding this type into their own
 // client-specific option wrapper. See example for usage.