How to transform Streaming Replication Master-Slave to Cascaded Master-Slave1-Slave2 setup?

I've setup streaming replication as part of HA solution on my production enviroment. I've two ubuntu servers PROD1 and PROD2. PROD1 is master and PROD2 is slave. In case of failover the slave database on PROD2 would be promoted to master database.

What I want is to make the slave database (on PROD2) to upstream server and setup another database on PROD1 as downstream server. The idea is to use the upstream server in case of failover and downstream server in case of fallback.

Please advise what configuration changes would be required to achive the above.

Thanks