[#335] added Discord OAuth2 provider

tools/auth/auth_test.go

@@ -54,4 +54,13 @@ func TestNewProviderByName(t *testing.T) {
 	if _, ok := p.(*auth.Gitlab); !ok {
 		t.Error("Expected to be instance of *auth.Gitlab")
 	}
+
+	// discord
+	p, err = auth.NewProviderByName(auth.NameDiscord)
+	if err != nil {
+		t.Errorf("Expected nil, got error %v", err)
+	}
+	if _, ok := p.(*auth.Discord); !ok {
+		t.Error("Expected to be instance of *auth.Discord")
+	}
 }