Not really addressing your problem, but it is super easy to use SSL with docker xwiki tomcat image (and I can confirm that file upload works). Just map two extra volumes: keystore and server.xml files.
add to server.xml
<!-- Define TLS connector for xwiki -->
<Connector port="8443" protocol="org.apache.coyote.http11.Http11Nio2Protocol" sslImplementationName="org.apache.tomcat.util.net.jsse.JSSEImplementation" maxThreads="150" SSLEnabled="true" scheme="https" secure="true" defaultSSLHostConfigName="*.example.com">
<SSLHostConfig protocols="TLSv1.2,+TLSv1.3" hostName="*.example.com">
<Certificate certificateKeystoreFile="conf/xwiki.keystore.pkcs12" certificateKeystorePassword="*****" certificateKeyAlias="xwiki" certificateKeyPassword="*****" certificateKeystoreType="PKCS12" type="RSA" />
</SSLHostConfig>
</Connector>
sudo docker run -d --net=xwiki-nw --name xwiki-ssl --restart=always --expose=8443 -p 192.168.1.100:443:8443 -v /home/zzz/xwiki/xwiki:/usr/local/xwiki -v /home/zzz/xwiki/server.xml:/usr/local/tomcat/conf/server.xml -v /home/zzz/xwiki/xwiki_web.keystore.pkcs12:/usr/local/tomcat/conf/xwiki.keystore.pkcs12 -e DB_USER=xwiki -e DB_PASSWORD=***** -e DB_DATABASE=xwiki -e DB_HOST=xwiki-mysql xwiki:11-mysql-tomcat