@Override
    @CanIgnoreReturnValue
    public AuthenticationHandlerExecutionResult addWarning(final MessageDescriptor message) {
        this.warnings.add(message);
        return this;
    }
List of warnings issued by the authentication source while authenticating the credential.
core/cas-server-core-authentication-api/src/main/java/org/apereo/cas/authentication/DefaultAuthenticationHandlerExecutionResult.java