protected String computeSloKey(final String sessionIndex, final SAML2AuthenticationCredentials.SAMLNameID nameId) {
        if (sessionIndex != null) {
            return sessionIndex;
        }

        if (nameId != null) {
            return nameId.getValue();
        }

        return null;
    }
<p>computeSloKey.</p>

@param sessionIndex a {@link String} object
@param nameId a {@link SAML2AuthenticationCredentials.SAMLNameID} object
@return a {@link String} object
pac4j-saml/src/main/java/org/pac4j/saml/profile/impl/AbstractSAML2ResponseValidator.java