fix error handling

Author: hickford

deviceauth.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	"golang.org/x/net/context/ctxhttp"
+	"golang.org/x/oauth2/internal"
 )
 
 const (
@@ -77,5 +78,9 @@ func parseError(err error) string {
 		_ = json.Unmarshal(e.Body, &eResp)
 		return eResp["error"]
 	}
+	e2, ok := err.(*internal.TokenError)
+	if ok {
+		return e2.Err
+	}
 	return ""
 }

oauth2.go

@@ -275,7 +275,7 @@ func (c *Config) Poll(ctx context.Context, da *DeviceAuth, opts ...AuthCodeOptio
 		case errAccessDenied, errExpiredToken:
 			return tok, errors.New("oauth2: " + errTyp)
 		case errSlowDown:
-			interval += 1
+			interval += 5
 			fallthrough
 		case errAuthorizationPending:
 		}