Merge pull request #1 from Dainismo/feature/add_token_refresh_handler

Added token refresh callback

oauth2.go

@@ -318,7 +318,11 @@ func (s *reuseTokenSource) Token() (*Token, error) {
 		return nil, err
 	}
 	t.expiryDelta = s.expiryDelta
+	t.OnTokenRefresh = s.t.OnTokenRefresh
 	s.t = t
+	if t.OnTokenRefresh != nil {
+		t.OnTokenRefresh(*t)
+	}
 	return t, nil
 }
 

token.go

@@ -49,6 +49,10 @@ type Token struct {
 	// mechanisms for that TokenSource will not be used.
 	Expiry time.Time `json:"expiry,omitempty"`
 
+	// OnTokenRefresh is a function that's getting called whenever
+	// the TokenSource refreshed the Token.
+	OnTokenRefresh func(t Token)
+
 	// raw optionally contains extra metadata from the server
 	// when updating a token.
 	raw interface{}