SSL certificates per domain

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This article applies to the following ZCS versions.
  ZCS 7.0 Article  ZCS 7.0
  ZCS 8.0 Article  ZCS 8.0


Contents


This document explains how to add per domain cert on a ZCS running 7.x version.

Until ZCS 6.x, per domain ssl certificate or multiple ssl certificates on a single ZCS was not supported. RFE #8128. This feature has been introduced in ZCS 7.x.

In this example, I am adding a new domain called example.com and deploying a new certificate for example.com.

Prerequisites

  • Zimbra proxy service must be installed and enabled on the server. In multi server environment, do these steps on the proxy node.
  • You should have a signed certificate + matching key pair and the trusted chain certs from your CA (Certificate Authority) .
  • You will need to add ipv4 addresses per domain which will pair to the respective domain name. For example:
 1.1.1.1 => example.com
 2.2.2.2 => otherdomain.com
 3.3.3.3 => yetanotherdomain.com

Configure Zimbra Proxy Server

1. Make sure Zimbra proxy service is configured correctly and serving https. If not, configure proxy now, run following as zimbra. It will set "zimbraReverseProxyMailMode" to both.

 su - zimbra
 /opt/zimbra/libexec/zmproxyconfig -m -w -e -x both -H `zmhostname`

2. Restart proxy service

 zmproxyctl stop;zmproxyctrl start
  • If its already configured - skip to next section.

Configuring IP address and domain

1. Add a new ipv4 address to the server which will pair to name example.com (via the example virtual hostname mail.example.com). You can do it using IP address aliasing. For example, the new address can be assigned to eth0:1 device. Lets consider the new ipv4 address is 1.2.3.4 which should be an A record for mail.example.com. The IP address could be public (if server is on Internet) or internal (if the server is behind firewall/NAT'ed).

2. Add the new domain example.com. Set zimbraVirtualHostName to mail.example.com and zimbraVirtualIPAddress to 1.2.3.4. Make sure the zimbraVirtualHostName is set to the name which will be used to access the domain (URL) and the SSL certificate is signed for same name.

 zmprov cd example.com zimbraVirtualHostName "mail.example.com" zimbraVirtualIPAddress "1.2.3.4"

NOTE: If the server is behind firewall and NAT'ed with external address, make sure the external requests for "mail.example.com" hits the aliased IP address and not the actual local IP of server.

Verifying and Preparing the Certificates

We have three files received from the CA. The server (domain) certificate, two chain certs. And we have existing key file (which was used to generate the csr)

1. Save the example.com certificate, key and chain files to a directory /tmp/example.com. You can receive single or multiple chain certs from your CA. Here we have two chain certs from the CA. i.e. example.com.root.crt and example.com.intermediate.crt.

 ls /tmp/example.com
 example.com.key
 example.com.crt
 example.com.root.crt
 example.com.intermediate.crt

2. Add the chain certs to a single file called example.com_ca.crt

 cat example.com.root.crt example.com.intermediate.crt >> example.com_ca.crt

3. Confirm if the key and certificate matches and chain certs completes the trust.

 /opt/zimbra/bin/zmcertmgr verifycrt comm /tmp/example.com/example.com.key /tmp/example.com/example.com.crt /tmp/example.com/example.com_ca.crt
  • Check the output, it should say something like this. If not, make sure you have correct key and chain cert files.
 ** Verifying example.com.crt against example.com.key
 Certificate (example.com.crt) and private key (example.com.key) match.
 Valid Certificate: example.com.crt: OK

Deploying the Certificate on domain

1. Add the domain certificate and chain files to a single file called example.com.bundle

 cat example.com.crt example.com_ca.crt >> example.com.bundle

2. Run following to save the certificates and key in ldap database.

 /opt/zimbra/libexec/zmdomaincertmgr savecrt example.com example.com.bundle example.com.key
  • The syntax is:
 /opt/zimbra/libexec/zmdomaincertmgr savecrt <domainname> <certificate with chain certs> <keyfile>

3. Run following to deploy the domain certificate. This will save the certificate and key as /opt/zimbra/conf/domaincerts/example.com

 /opt/zimbra/libexec/zmdomaincertmgr deploycrts

4. Make sure the example.com is resolving to its local IP address from Zimbra host. Or make an similar entry in /etc/hosts file.

 1.2.3.4      example.com

5. Restart proxy service to take the changes in effect.

 zmproxyctl stop; zmproxyctl start

6. Once the restart is successfull, try to access the domain using the URL which is set in "zimbraVirtualHostName" over https. And check the certificate loaded in the browser. In this case the URL will be https://example.com

Testing

Run this command locally on zimbra server to check if the correct domain cert is offered while accessing the domain with "zimbraVirtualHostName" or "zimbraVirtualIPAddress"

 openssl s_client -connect example.com:443
 openssl s_client -connect 1.2.3.4:443

Troubleshooting

  • If you do not see domain cert by accessing the domain with its zimbraVirtualHostName (example.com). Make sure the https connection from Internet/intranet is going to server's local IP address which is defined in zimbraVirtualIPAddress.
  • If the proxy startup gives following error, try to change the order of certificates in /opt/zimbra/conf/domaincerts/example.com.crt file and restart proxy.
 Starting nginx...nginx: [emerg] SSL_CTX_use_PrivateKey_file("/opt/zimbra/conf/domaincerts/example.com.key") failed (SSL: error:0B080074:x509 certificate 
 routines:X509_check_private_key:key values mismatch)
  • If you are using multiple proxy servers or adding new proxy servers, make sure you copy all the contents of /opt/zimbra/conf/domaincerts/ among all proxy servers. Otherwise proxy service will fail to start.

Verified Against: ZCS 7.0 Date Created: 01/15/2014
Article ID: http://wiki.zimbra.com/index.php?title=SSL_certificates_per_domain Date Modified: 10/17/2014
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