docs: add example to extract HEX encoded fingerprint from certificate (…

…#33507) (#33680)

This commit adds an example of how to extract the HEX encoded SHA-256
fingerprint from a CA certificate using openssl, awk and sed. Those
tools should be available on most Unix-like systems.

Co-authored-by: DeDe Morton <dede.morton@elastic.co>
(cherry picked from commit 0ebad69)

Co-authored-by: Tiago Queiroz <tiago.queiroz@elastic.co>

libbeat/docs/shared-ssl-config.asciidoc

@@ -386,6 +386,14 @@ present in the chain during the handshake, it will be added to the
 `certificate_authorities` list and the handshake will continue
 normaly.
 
+To get the fingerprint from a CA certificate on a Unix-like
+system, you can use the following command, where `ca.crt` is the
+certificate.
+
+[source]
+------------------------
+openssl x509 -fingerprint -sha256 -noout -in ./ca.crt | awk --field-separator="=" '{print $2}' | sed 's/://g'
+------------------------
 
 [discrete]
 [[ssl-server-config]]