I have configured FBA with SharePoint 2013. It works well without any issues. But when any user enters wrong username or password and login fails, then below error gets posted in event viewer on server:
The security token username and password could not be validated.
This does not cause any issues in the system, but I don't want this error to be recorded because this is not an error actually, this is something like user can't access the system because of invalid credentials.
As FBA works perfectly with correct user credentials, there is not any issue in membership provider or role provider configuration in web.config files.