Magento 2.3.4 - Check the detail error about the error

Eg: Customer login error: An unspecified error occurred. Please contact us for assistance

If you want the more detail about the error

 Go to file

vendor/magento/module-customer/Controller/Account/LoginPost.php

and put these lines 

    $message = $e->getMessage();
    $this->messageManager->addError($message);

just before lines- 

    $this->messageManager->addError(
                            __('An unspecified error occurred. Please contact us for assistance.')
                        );

now on front try to log in and check error.