public static String getUserIdFromIdentities(final JwtClaims jwtClaims) {
        String userId = null;
        final String identities = (String) jwtClaims.getClaimValue(IDENTITIES);
        if (identities != null) {
            userId = getUserIdFromIdentities(identities);
        }
        return userId;
    }
Gets the unique ID that links the identity on the IDP to the stroom_user.
Maps to the 'name' column in stroom_user table.
stroom-security/stroom-security-common-impl/src/main/java/stroom/security/common/impl/JwtUtil.java