mod_proxy_ajp: Forward SSL protocol name (SSLv3, TLSv1.1 etc.) as a request attribute to the backend. The name is taken from the SSL_PROTOCOL env var. Recent Tomcat versions will extract it and provide it as a servlet request attribute named "org.apache.tomcat.util.net.secure_protocol_version".
The change is compatible with existing AJP13, because we forward the protocol name as a normal named attribute, not with a new byte abbreviated attribute name.