chore: remove build tags for go versions < 1.15

option/option.go

@@ -10,6 +10,7 @@ import (
 	"net/http"
 
 	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google"
 	"google.golang.org/api/internal"
 	"google.golang.org/api/internal/impersonate"
 	"google.golang.org/grpc"
@@ -328,3 +329,14 @@ func (i impersonateServiceAccount) Apply(o *internal.DialSettings) {
 	o.ImpersonationConfig.Delegates = make([]string, len(i.delegates))
 	copy(o.ImpersonationConfig.Delegates, i.delegates)
 }
+
+type withCreds google.Credentials
+
+func (w *withCreds) Apply(o *internal.DialSettings) {
+	o.Credentials = (*google.Credentials)(w)
+}
+
+// WithCredentials returns a ClientOption that authenticates API calls.
+func WithCredentials(creds *google.Credentials) ClientOption {
+	return (*withCreds)(creds)
+}

transport/dial.go

@@ -8,8 +8,10 @@ import (
 	"context"
 	"net/http"
 
+	"golang.org/x/oauth2/google"
 	"google.golang.org/grpc"
 
+	"google.golang.org/api/internal"
 	"google.golang.org/api/option"
 	gtransport "google.golang.org/api/transport/grpc"
 	htransport "google.golang.org/api/transport/http"
@@ -34,3 +36,13 @@ func DialGRPC(ctx context.Context, opts ...option.ClientOption) (*grpc.ClientCon
 func DialGRPCInsecure(ctx context.Context, opts ...option.ClientOption) (*grpc.ClientConn, error) {
 	return gtransport.DialInsecure(ctx, opts...)
 }
+
+// Creds constructs a google.Credentials from the information in the options,
+// or obtains the default credentials in the same way as google.FindDefaultCredentials.
+func Creds(ctx context.Context, opts ...option.ClientOption) (*google.Credentials, error) {
+	var ds internal.DialSettings
+	for _, opt := range opts {
+		opt.Apply(&ds)
+	}
+	return internal.Creds(ctx, &ds)
+}

transport/http/dial.go

@@ -210,3 +210,14 @@ func addOCTransport(trans http.RoundTripper, settings *internal.DialSettings) ht
 		Propagation: &propagation.HTTPFormat{},
 	}
 }
+
+// clonedTransport returns the given RoundTripper as a cloned *http.Transport.
+// It returns nil if the RoundTripper can't be cloned or coerced to
+// *http.Transport.
+func clonedTransport(rt http.RoundTripper) *http.Transport {
+	t, ok := rt.(*http.Transport)
+	if !ok {
+		return nil
+	}
+	return t.Clone()
+}