In /var/lib/tomcat-proxycas/conf/server.xml, find the place where the HTTP connector is defined, and change it into:
<Connector port="8180" protocol="HTTP/1.1"
connectionTimeout="20000"
URIEncoding="UTF-8"
redirectPort="8443" />
<Connector port="8443" protocol="HTTP/1.1"
SSLEnabled="true"
scheme="https"
secure="true"
URIEncoding="UTF-8"
maxThreads="150"
clientAuth="false"
keystoreFile="/etc/tomcat6/keystore"
keystorePass="STOREPASSWORD"
compression="on"
compressionMinSize="2048"
noCompressionUserAgents="gozilla, traviata"
compressableMimeType="text/html,text/xml,application/xml,text/javascript,application/x-javascript,application/javascript,text/css" />
... in which you also take care of changing the STOREPASSWORD string.
il suffit donc de remplacer STOREPASSWORD par mdpstore dans mon cas...