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The following page has been changed by DanPoirier: http://wiki.apache.org/httpd/NameBasedSSLVHostsWithSNI New page: = SSL with Virtual Hosts Using SNI = == Summary == Using name-based virtual hosts with SSL adds another layer of complication. Without the SNI extension, it's not generally possible (though a subset of virtual host might work). With SNI, it's necessary to consider the configuration carefully to ensure security is maintained. == The Problem == The problem with using named virtual hosts over SSL is that named virtual hosts rely on knowing what hostname is being requested, and the request can't be read until the SSL connection is established. The ordinary behavior, then, is that the SSL connection is set up using the configuration in the default virtual host for the address where the connection was received. While Apache can renegotiate the SSL connection later after seeing the hostname in the request (and does), that's too late to pick the right server certificate to use to match the request hostname during the initial handshake, resulting in browser warnings/errors about certificates having the wrong hostname in them. And while it's possible to put multiple hostnames in a modern certificate and just use that one certificate in the default vhost, there are many hosting providers who are hosting far too many sites on a single address for that to be practical for them. == Server Name Indication == The solution is an extension to the SSL protocol called '''Server Name Indication''' ([http://www.ietf.org/rfc/rfc4366.txt RFC 4366]), which allows the client to include the requested hostname in the first message of its SSL handshake (connection setup). This allows the server to determine the correct named virtual host for the request and set the connection up accordingly from the start. == Prerequisites to use SNI == * Use OpenSSL 0.9.8f or later * Build OpenSSL with the TLS Extensions option enabled (option enable-tlsext; OpenSSL 0.9.9 might have this enabled by default). * Apache must have been built with that OpenSSL (./configure --with-ssl=/path/to/your/openssl). In that case, mod_ssl will automatically detect the availability of the TLS extensions and support SNI. * Apache must use that OpenSSL at run-time, which might require setting LD_LIBRARY_PATH or equivalent to point to that OpenSSL, maybe in bin/envvars. (You'll get unresolved symbol errors at Apache startup if Apache was built with SNI but isn't finding the right openssl libraries at run-time.) How can you tell if your Apache build supports SNI? If you configure multiple name-based virtual hosts for an address where SSL is configured, and SNI isn't built into your Apache, then upon Apache startup a message like "You should not use name-based virtual hosts in conjunction with SSL!!" will occur in the error log. If SNI is built in, then the error log will show "[warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366)". The client browser must also support SNI. Here are some browsers that do: * Mozilla Firefox 2.0 or later * Opera 8.0 or later (with TLS 1.1 enabled) * Internet Explorer 7.0 or later (on Vista, not XP) * Google Chrome * Safari 3.2.1 on Mac OS X 10.5.6 (per [http://en.wikipedia.org/wiki/Server_Name_Indication#Browsers Wikipedia]) == Changes in configuration to use SNI == There aren't any new directives related to SNI. The first (default) vhost for SSL name-based virtual hosts '''must''' include TLSv1 as a permitted protocol, otherwise Apache will not accept the SNI information from the client and it will be as if the client did not support SNI at all. Since the first (default) vhost will be used for any request where the provided server name doesn't match another vhost, it is important that the first vhost have the most restrictive access control, otherwise clients can access restricted resources by sending a request for any unknown hostname. (This isn't actually any different from using virtual hosts without SSL.) == Environment variables == When Apache supports SNI and the client provided the hostname using SNI, the new environment variable SSL_TLS_SNI will be set to the hostname that the client provided. == Scenarios == === SNI/Request hostname mismatch, or SNI provides hostname and request doesn't. === This is a browser bug. Apache will reject the request with a 400-type error. === Client doesn't support SNI. === If Apache has SNI support, and a request without the SNI hostname is received for a name-based virtual host over SSL, it will be rejected (403) and this message logged: {{{ [error] No hostname was provided via SNI for a name based virtual host }}} == Examples == === Server configuration === {{{ # Ensure that Apache listens on port 443 Listen 443 # Listen for virtual host requests on all IP addresses NameVirtualHost *:443 <VirtualHost *:443> # Because this virtual host is defined first, it will # be used as the default if the hostname is not received # in the SSL handshake, e.g. if the browser doesn't support # SNI. DocumentRoot /www/example1 ServerName www.example.com # Other directives here </VirtualHost> <VirtualHost *:443> DocumentRoot /www/example2 ServerName www.example.org # Other directives here </VirtualHost> }}}
