Elytron HTTP DIGEST authentication comply to rfc2617 - which means MD5 is used by default (it means it is hardcode, with no way to configure another hash algorithm). But MD5 could make troubles in fips environment [5].

        String algorithm = convertToken(ALGORITHM, responseTokens.get(ALGORITHM));
        if (MD5.equals(algorithm) == false) {
            throw log.mechUnsupportedAlgorithm(getMechanismName(), algorithm);
        }

There exists proposed rfc7616 which makes algorithm configurable, work on new DIGEST features are covered by [1]. dlofthouse is it planned for [1] to target 7.1?

[1] https://issues.jboss.org/browse/ELY-286
[2] https://developer.jboss.org/wiki/ElytronHTTPDigestNonceHandling-Design
[3] https://tools.ietf.org/html/rfc2617
[4] https://tools.ietf.org/html/rfc7616
[5] https://access.redhat.com/support/cases/#/case/01761455