Switch from govendor to go modules. (#587)

Thanks to @BenoitKnecht for leading the way on this.

vendor/golang.org/x/oauth2/token.go

@@ -5,13 +5,14 @@
 package oauth2
 
 import (
+	"context"
+	"fmt"
 	"net/http"
 	"net/url"
 	"strconv"
 	"strings"
 	"time"
 
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2/internal"
 )
 
@@ -20,7 +21,7 @@ import (
 // expirations due to client-server time mismatches.
 const expiryDelta = 10 * time.Second
 
-// Token represents the crendentials used to authorize
+// Token represents the credentials used to authorize
 // the requests to access protected resources on the OAuth 2.0
 // provider's backend.
 //
@@ -117,13 +118,16 @@ func (t *Token) Extra(key string) interface{} {
 	return v
 }
 
+// timeNow is time.Now but pulled out as a variable for tests.
+var timeNow = time.Now
+
 // expired reports whether the token is expired.
 // t must be non-nil.
 func (t *Token) expired() bool {
 	if t.Expiry.IsZero() {
 		return false
 	}
-	return t.Expiry.Add(-expiryDelta).Before(time.Now())
+	return t.Expiry.Round(0).Add(-expiryDelta).Before(timeNow())
 }
 
 // Valid reports whether t is non-nil, has an AccessToken, and is not expired.
@@ -150,9 +154,25 @@ func tokenFromInternal(t *internal.Token) *Token {
 // This token is then mapped from *internal.Token into an *oauth2.Token which is returned along
 // with an error..
 func retrieveToken(ctx context.Context, c *Config, v url.Values) (*Token, error) {
-	tk, err := internal.RetrieveToken(ctx, c.ClientID, c.ClientSecret, c.Endpoint.TokenURL, v)
+	tk, err := internal.RetrieveToken(ctx, c.ClientID, c.ClientSecret, c.Endpoint.TokenURL, v, internal.AuthStyle(c.Endpoint.AuthStyle))
 	if err != nil {
+		if rErr, ok := err.(*internal.RetrieveError); ok {
+			return nil, (*RetrieveError)(rErr)
+		}
 		return nil, err
 	}
 	return tokenFromInternal(tk), nil
 }
+
+// RetrieveError is the error returned when the token endpoint returns a
+// non-2XX HTTP status code.
+type RetrieveError struct {
+	Response *http.Response
+	// Body is the body that was consumed by reading Response.Body.
+	// It may be truncated.
+	Body []byte
+}
+
+func (r *RetrieveError) Error() string {
+	return fmt.Sprintf("oauth2: cannot fetch token: %v\nResponse: %s", r.Response.Status, r.Body)
+}