public static Optional<String> getClaimValue(final JwtContext jwtContext, final String claim) {
        try {
            return NullSafe.getAsOptional(
                    jwtContext,
                    JwtContext::getJwtClaims,
                    ThrowingFunction.unchecked(jwtClaims ->
                            jwtClaims.getClaimValue(claim, String.class)));
        } catch (Exception e) {
            LOGGER.debug(() -> LogUtil.message("Error getting claim {}: {}", claim, e.getMessage()), e);
            return Optional.empty();
        }
    }
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