How to hide processLogin exception

I have a spring server which communicates with third party service to login. Issue is that if the third part is down there is some nasty expection appear on client browser:

<form-login login-page="/auth/login" 
        default-target-url="/alerts/#"
        always-use-default-target="false"
        authentication-success-handler-ref="P8AuthenticationSuccessHandler"
        authentication-failure-handler-ref="authFailureHandler"
        login-processing-url="/auth/processLogin"
        password-parameter="password"
        username-parameter="username"/>

I want to hide this exception from user. How can I do this?