This playbook contains the default client certificate and key which were disrtibuted as part of Alfresco 4.x and 5.x (for Solr 1.4 & Solr 4). Those certificates have been generated long ago and security requirement have largely evolved since then. Running the playbook on modern distribution of Linux, you may encounter errors like:
140AB18F:SSL routines:SSL_CTX_use_certificate:ee key too small
This is because your Linux distribution prevent you from using this client certificate (Distros shipping OpenSSL 1.1.1a-pre9 and beyond).
This client certificate is now very old and uses key length which are considered weak. You should really consider using certificates from your own PKI instead!
If you still need to use that certificate on modern Linux, you will need to lessen the security of the distribution. For example on Debian-like systems: https://wiki.debian.org/ContinuousIntegration/TriagingTips/openssl-1.1.1
If use your own PKI or you have re-generated the Solr certificates (as recommanded by Alfresco), you'll need to provide the client certificate and key in unencrypted PEM format. Conversion can be done using openssl:
$ openssl pkcs12 -in yml/roles/solr/files/mypkicert.p12 -nokeys -clcerts -out yml/roles/solr/files/mypkicert.crt
$ openssl pkcs12 -in yml/roles/solr/files/mypkicert.p12 -nocerts -nodes -out yml/roles/solr/files/mypkicert.key
You can also use a single file for both certificate and key and only specify solr_client_cert configuration variable:
$ openssl pkcs12 -in mypkicert.p12 -clcerts -nodes -out mypkicert.pem