Lync 2013 certificate requirements for multiple SIP domains

Question

Hi All,
I am engaged with a client in respect of a Lync 2013 implementation initially as a conferencing platform with a view to enabling EV functions (inc. PSTN conferencing) in the future. They initially need to support 30 SIP domains and eventually
around 100 SIP domains which is proving to be either not possible or severely cost prohibitive. Their current certificate provider, Thawte, can only support up to 25 SANs and have quoted them 5 figures. We tend to use GeoTrust as they are cheaper but they
appear to have a limit of 25 SANs. GoDaddy appear to support up to 100 SANs for a pretty reasonable cost. My questions are as follows:
Is there a way that I’m missing of reducing the number of SANs required on the Edge server?
Use aliases for access edge FQDNs - Supported by desktop client but not by other devices so not really workable
Don’t support XMPP federation therefore removing the need for domain name FQDNs for each SIP domain
Is there a way that I’m missing of reducing the number of SANs required on the Reverse Proxy server?
Friendly URL option 3 from this page:
http://technet.microsoft.com/en-us/library/gg398287.aspx
Client auto-configuration:
i.     
Don’t support mobile client auto-configuration in which case no lyncdiscover.sipdomain1.com DNS records or SANs would be required.
ii.     
Support mobile client auto-configuration over HTTP only in which case CNAME records are required for each SIP domain (lyncdiscover.sipdomain1.com, etc. pointing to lyncdiscover.designateddomain.com) but no SANs are required.
iii.     
Support mobile client auto-configuration over HTTPS in which case DNS records are required for each SIP domain and a SAN entry for each SIP domains is also required. This is because a DNS CNAME to another domain is not supported over
HTTPS.
If the answer to 1 and/or 2 is no, are there certificate providers that support over 100 SANs?
How do certificate requirements differ when using the Lync 2013 hosting pack? I would think that this issue is something that a hosting provider would need to overcome.
Would the Lync 2013 Hosting Pack work for this customer? The customer uses SPLA licensing so I think is eligible to use the hosting pack but not 100% sure it will work in their environment given that client connections are supposed
to all come through the Edge where their tenants will be internal and also given the requirement for an ACP for PSTN conferencing.
Many thanks,

Answer 1

Many thanks for the response.
I was already planning to use option 3 from the below page for simple URLs to cut down on SAN requirement.
http://technet.microsoft.com/en-us/library/gg398287.aspx
What are the security concerns for publishing autodiscover over port 80? I.e. Is this only used for the initial download of the discovery record and then HTTPS is used for authentication? This seems to be the case from the following note on the below page:
http://technet.microsoft.com/en-gb/library/hh690030.aspx
Mobile device clients do not support multiple Secure Sockets Layer (SSL) certificates from different domains. Therefore, CNAME redirection to different domains is not supported over HTTPS. For example, a DNS CNAME record for lyncdiscover.contoso.com that redirects
to an address of director.contoso.net is not supported over HTTPS.
In such a topology, a mobile device client needs to use HTTP for the first request, so that the CNAME redirection is resolved over HTTP. Subsequent requests then use HTTPS. To support this scenario, you need to configure your reverse proxy with a web publishing
rule for port 80 (HTTP).
For details, see "To create a web publishing rule for port 80" in Configuring the Reverse Proxy for Mobility. CNAME redirection to the same domain is supported over HTTPS. In this case, the destination domain's certificate covers the originating
domain.”
I don’t think SRV records for additional SIP domain access edge is a workable solution as this is not supported by some devices.
As per the below article:
http://blog.schertz.name/2012/07/lync-edge-server-best-practices/
“The recommended approach for external client Automatic Sign-In when supporting multiple SIP domains is to include a unique Access Edge FQDN for each domain name in the SAN field.  This is no longer a requirement (it was in OCS) as it is possible to
create a DNS Service Locator Record (SRV) for each additional SIP domain yet have them all point back to the same original FQDN for the Access Edge service (e.g. sip.mslync.net). 
This approach will trigger a security alert in Windows Lync clients which can be accepted by the user, but some other clients and devices are unable to connect when the Automatic Sign-In process returns a pair of SRV and Host (A) records which do not share
the same domain namespace.  Thus it is still best practice to define a unique FQDN for each additional SIP domain and include that hostname in the external Edge certificate’s SAN field”.
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1. Basically the requirement is to initially provide Lync conferencing services (minus PSTN conferencing) to internal, external, federated and anonymous participants with a view to providing PSTN conferencing and therefore enterprise voice services later.
2. The customer currently supports close to 100 SMTP domains and wants to align their SIP domains with these existing domains. The structure of their business is such that “XXX IT Services” provide the IT infrastructure for a collection of companies who
fall under the XXX umbrella but are very much run as individual entities.
Question:
Would you agree that I’m going to need a SAN for every SIP domain’s access edge FQDN?
Thanks.