global class PortalPlugin extends Auth.ConnectedAppPlugin {

  // Return a user’s permission set assignments            
    global override Map<String,String> customAttributes (Id userId, Id connectedAppId, Map<String,String> formulaDefinedAttributes, Auth.InvocationContext context) {  

        User userToUpd = [Select Id, TPP_TokenPT__c from User where id = :userId][0];
        if(String.isNotBlank(userToUpd.TPP_TokenPT__c))
        {
            userToUpd.TPP_TokenPT__c = '';
            update userToUpd;
        }

        System.debug(formulaDefinedAttributes);

        return formulaDefinedAttributes;     
    } 
}