OCSP multi stapling : how to enable it? Simple stapling is OK

Question

I would like to set up OCSP multi stapling and I can not find a lot of documentation on it, or in any case, recent information.

I have a root certificate authority (CA) and a daughter CA below. Both work with Freeipa (and Freeipa uses Dogtag). I have a https server too.

1. The root CA issues a certificate for the daughter CA.
2. The daughter CA issues a certificate for the https server.
3. The https server delivers the service for an external client.

OCSP simple stapling works : the client can check the certificate for the https server. Now, I would like to check the no-revocation of the daughter CA by stapling too.

My https server is Apache. On it, I have added the lines following in /etc/httpd/conf.d/ssl.conf :

SSLUseStapling on  
SSLStaplingCache shmcb:/run/httpd/sslcache(512000)

And, always in ssl.conf on the https server, I used the SSLCertificateChainFile with a PEM file containing the daughter CA's certificate and the https server's certificate.

I assume it is not enough to add the root CA's certificate in the PEM file.
And the https server must present a certificate with the urls of both CAs written in the field Authority Information Access. It needs some configuration.

What should I add to simple stapling?
And how to check that it works?
Does Freeipa/Dogtag support OCSP multi stapling?

Subsidiary question: is multi stapling supported by browsers?
I guess so because it is common to have a hierarchy of CAs in the internet world but I would like to have more details and I understood that it's little used.

Thank you very much!

Answer 1

To be clear, the CA (or its delegate) must support (plain) OCSP, but the server must support stapling, either single or multi (aka v2).

From http://httpd.apache.org/docs/2.4/mod/mod_ssl.html at SSLUseStapling, with emphasis added:

This option enables OCSP stapling, as defined by the "Certificate Status Request" TLS extension specified in RFC 6066. If enabled (and requested by the client), mod_ssl will include an OCSP response for its own certificate in the TLS handshake. Configuring an SSLStaplingCache is a prerequisite for enabling OCSP stapling.

OCSP stapling relieves the client of querying the OCSP responder on its own, but it should be noted that with the RFC 6066 specification, the server's CertificateStatus reply may only include an OCSP response for a single cert. For server certificates with intermediate CA certificates in their chain (the typical case nowadays), stapling in its current implementation therefore only partially achieves the stated goal of "saving roundtrips and resources" - see also RFC 6961 (TLS Multiple Certificate Status Extension).

(Although this is ambiguously worded, 'may only include [one]' for 6066 means 'it is only able/allowed to include one' not 'it is possible it only includes one'.)

So, it looks like you can't. Although I'm pretty sure mod_ssl is open-source, so you could implement a change to it yourself if you really want.