pjsip: clarify tls cert and key file usage

A question arose as to whether a .pem file
could be provided in place of the .crt and
.key files in a PJSIP TLS configuration. I
tested this and discovered that although a
cert will be read from the pem file, a key
will not, and thus the priv_key_file entry
is still required. This update to the fine
documentation clarifies the option usage.

AST-1448 #close
Review: https://reviewboard.asterisk.org/r/4129/
Reported by: John Bigelow
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Merged revisions 426928 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 426930 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@426932 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/samples/pjsip.conf.sample

@@ -747,7 +747,10 @@
         ; "")
 ;ca_list_file=  ; File containing a list of certificates to read TLS ONLY
                 ; (default: "")
-;cert_file=     ; Certificate file for endpoint TLS ONLY (default: "")
+;cert_file=     ; Certificate file for endpoint TLS ONLY
+                ; Will read .crt or .pem file but only uses cert,
+                ; a .key file must be specified via priv_key_file
+                ; (default: "")
 ;cipher=        ; Preferred cryptography cipher names TLS ONLY (default: "")
 ;domain=        ; Domain the transport comes from (default: "")
 ;external_media_address=        ; External IP address to use in RTP handling

res/res_pjsip.c

@@ -821,6 +821,12 @@
 				</configOption>
 				<configOption name="cert_file">
 					<synopsis>Certificate file for endpoint (TLS ONLY)</synopsis>
+					<description><para>
+						A path to a .crt or .pem file can be provided.  However, only
+						the certificate is read from the file, not the private key.
+						The <literal>priv_key_file</literal> option must supply a
+						matching key file.
+					</para></description>
 				</configOption>
 				<configOption name="cipher">
 					<synopsis>Preferred cryptography cipher names (TLS ONLY)</synopsis>