google: don't check for IsNotExist for well-known file

There are cases when reading this file that a ENOTDIR is returned.
Because of this it is safer to just fall-back when any error
happens from reading the gcloud file.

Change-Id: Ie8e45ad508643e900adb5c9787907aaa50cceb5d
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/493695
Run-TryBot: Cody Oss <codyoss@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Cody Oss <codyoss@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

google/default.go

@@ -8,7 +8,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -142,10 +141,8 @@ func FindDefaultCredentialsWithParams(ctx context.Context, params CredentialsPar
 
 	// Second, try a well-known file.
 	filename := wellKnownFile()
-	if creds, err := readCredentialsFile(ctx, filename, params); err == nil {
-		return creds, nil
-	} else if !os.IsNotExist(err) {
-		return nil, fmt.Errorf("google: error getting credentials using well-known file (%v): %v", filename, err)
+	if b, err := os.ReadFile(filename); err == nil {
+		return CredentialsFromJSONWithParams(ctx, b, params)
 	}
 
 	// Third, if we're on a Google App Engine standard first generation runtime (<= Go 1.9)
@@ -231,7 +228,7 @@ func wellKnownFile() string {
 }
 
 func readCredentialsFile(ctx context.Context, filename string, params CredentialsParams) (*Credentials, error) {
-	b, err := ioutil.ReadFile(filename)
+	b, err := os.ReadFile(filename)
 	if err != nil {
 		return nil, err
 	}