oauth2: don't use http.DefaultTransport.

http.DefaultTransport is not available on App Engine.

google/appengine.go

@@ -8,6 +8,7 @@ import (
 	"github.com/golang/oauth2"
 
 	"appengine"
+	"appengine/urlfetch"
 )
 
 // AppEngineConfig represents a configuration for an
@@ -26,7 +27,12 @@ func NewAppEngineConfig(context appengine.Context, scopes []string) *AppEngineCo
 // NewTransport returns a transport that authorizes
 // the requests with the application's service account.
 func (c *AppEngineConfig) NewTransport() oauth2.Transport {
-	return oauth2.NewAuthorizedTransport(c, nil)
+	transport := &urlfetch.Transport{
+		Context:                       c.context,
+		Deadline:                      0,
+		AllowInvalidServerCertificate: false,
+	}
+	return oauth2.NewAuthorizedTransport(transport, c, nil)
 }
 
 // FetchToken fetches a new access token for the provided scopes.

google/appenginevm.go

@@ -3,6 +3,7 @@
 package google
 
 import (
+	"net/http"
 	"strings"
 
 	"github.com/golang/oauth2"
@@ -25,7 +26,7 @@ func NewAppEngineConfig(context appengine.Context, scopes []string) *AppEngineCo
 // NewTransport returns a transport that authorizes
 // the requests with the application's service account.
 func (c *AppEngineConfig) NewTransport() oauth2.Transport {
-	return oauth2.NewAuthorizedTransport(c, nil)
+	return oauth2.NewAuthorizedTransport(http.DefaultTransport, c, nil)
 }
 
 // FetchToken fetches a new access token for the provided scopes.

google/google.go

@@ -61,7 +61,7 @@ func NewComputeEngineConfig(account string) *ComputeEngineConfig {
 
 // NewTransport creates an authorized transport.
 func (c *ComputeEngineConfig) NewTransport() oauth2.Transport {
-	return oauth2.NewAuthorizedTransport(c, nil)
+	return oauth2.NewAuthorizedTransport(http.DefaultTransport, c, nil)
 }
 
 // FetchToken retrieves a new access token via metadata server.
@@ -76,7 +76,7 @@ func (c *ComputeEngineConfig) FetchToken(existing *oauth2.Token) (token *oauth2.
 		return
 	}
 	req.Header.Add("X-Google-Metadata-Request", "True")
-	resp, err := (&http.Client{Transport: oauth2.DefaultTransport}).Do(req)
+	resp, err := (&http.Client{}).Do(req)
 	if err != nil {
 		return
 	}