docs - Clarify how to use 'certificate' for servers (#36991) (#37006)

The docs didn't show where to put issuer certificate in the context
of TLS servers. This explains how to build up a PEM certificate bundle

(cherry picked from commit 009b3f0)

Co-authored-by: Andrew Kroh <[email protected]>

libbeat/docs/shared-ssl-config.asciidoc

@@ -443,42 +443,92 @@ certificate_authorities:
 [[server-certificate]]
 ==== `certificate: "/etc/server/cert.pem"`
 
-For server authentication, the path to the SSL authentication certificate must
-be specified for TLS. If the certificate is not specified, startup will fail.
+The end-entity (leaf) certificate that the server uses to identify itself.
+If the certificate is signed by a certificate authority (CA), then it should
+include intermediate CA certificates, sorted from leaf to root.
+For servers, a `certificate` and <<server-key,`key`>> must be specified.
 
-When this option is configured, the <<server-key,`key`>> option is also required.
-The certificate option support embedding of the certificate:
+The certificate option supports embedding of the PEM certificate content. This
+example contains the leaf certificate followed by issuer's certificate.
 
 [source,yaml]
 ----
 certificate: |
-    -----BEGIN CERTIFICATE-----
-    MIIDCjCCAfKgAwIBAgITJ706Mu2wJlKckpIvkWxEHvEyijANBgkqhkiG9w0BAQsF
-    ADAUMRIwEAYDVQQDDAlsb2NhbGhvc3QwIBcNMTkwNzIyMTkyOTA0WhgPMjExOTA2
-    MjgxOTI5MDRaMBQxEjAQBgNVBAMMCWxvY2FsaG9zdDCCASIwDQYJKoZIhvcNAQEB
-    BQADggEPADCCAQoCggEBANce58Y/JykI58iyOXpxGfw0/gMvF0hUQAcUrSMxEO6n
-    fZRA49b4OV4SwWmA3395uL2eB2NB8y8qdQ9muXUdPBWE4l9rMZ6gmfu90N5B5uEl
-    94NcfBfYOKi1fJQ9i7WKhTjlRkMCgBkWPkUokvBZFRt8RtF7zI77BSEorHGQCk9t
-    /D7BS0GJyfVEhftbWcFEAG3VRcoMhF7kUzYwp+qESoriFRYLeDWv68ZOvG7eoWnP
-    PsvZStEVEimjvK5NSESEQa9xWyJOmlOKXhkdymtcUd/nXnx6UTCFgnkgzSdTWV41
-    CI6B6aJ9svCTI2QuoIq2HxX/ix7OvW1huVmcyHVxyUECAwEAAaNTMFEwHQYDVR0O
-    BBYEFPwN1OceFGm9v6ux8G+DZ3TUDYxqMB8GA1UdIwQYMBaAFPwN1OceFGm9v6ux
-    8G+DZ3TUDYxqMA8GA1UdEwEB/wQFMAMBAf8wDQYJKoZIhvcNAQELBQADggEBAG5D
-    874A4YI7YUwOVsVAdbWtgp1d0zKcPRR+r2OdSbTAV5/gcS3jgBJ3i1BN34JuDVFw
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-    yvgJ38BRsFOtkRuAGSf6ZUwTO8JJRRIFnpUzXflAnGivK9M13D5GEQMmIl6U9Pvk
-    sxSmbIUfc2SGJGCJD4I=
-    -----END CERTIFICATE-----
+  -----BEGIN CERTIFICATE-----
+  MIIF2jCCA8KgAwIBAgIBAjANBgkqhkiG9w0BAQsFADBlMQswCQYDVQQGEwJVUzEW
+  MBQGA1UEBxMNU2FuIEZyYW5jaXNjbzEcMBoGA1UECRMTV2VzdCBFbCBDYW1pbm8g
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+  BDgwNoIJbG9jYWxob3N0ghFiZWF0cy5leGFtcGxlLmNvbYcEfwAAAYcQAAAAAAAA
+  AAAAAAAAAAAAATANBgkqhkiG9w0BAQsFAAOCAgEAldSZOUi+OUR46ERQuINl1oED
+  mjNsQ9FNP/RDu8mPJaNb5v2sAbcpuZb9YdnScT+d+n0+LMd5uz2g67Qr73QCpXwL
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+  puoJ9UYvfIcHUGPdZGU=
+  -----END CERTIFICATE-----
+  -----BEGIN CERTIFICATE-----
+  MIIFpjCCA46gAwIBAgIBATANBgkqhkiG9w0BAQsFADBlMQswCQYDVQQGEwJVUzEW
+  MBQGA1UEBxMNU2FuIEZyYW5jaXNjbzEcMBoGA1UECRMTV2VzdCBFbCBDYW1pbm8g
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+  RQQmEyTn1hn/eA==
+  -----END CERTIFICATE-----
 ----
 
 [float]
 [[server-key]]
 ==== `key: "/etc/server/cert.key"`
 
 The server certificate key used for authentication is required.
-The key option support embedding of the private key:
+The key option supports embedding of the private key:
 
 [source,yaml]
 ----