feat: allow custom username for new users

controller/oauth.go

@@ -237,6 +237,13 @@ func findOrCreateOAuthUser(c *gin.Context, provider oauth.Provider, oauthUser *o
 
 	// Set up new user
 	user.Username = provider.GetProviderPrefix() + strconv.Itoa(model.GetMaxUserId()+1)
+
+	if oauthUser.Username != "" {
+		if exists, err := model.CheckUserExistOrDeleted(oauthUser.Username, ""); err == nil && !exists {
+			user.Username = oauthUser.Username
+		}
+	}
+
 	if oauthUser.DisplayName != "" {
 		user.DisplayName = oauthUser.DisplayName
 	} else if oauthUser.Username != "" {