feat(Syslog): add documentation to secure the data collection to the …

…syslog forwarder

docs/xdr/features/collect/ingestion_methods/syslog/secured_forwarded.md

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+# How to secure data collection to the syslog forwarder
+
+## Overview
+
+Events are forwarded to Sekoia.io through a secured transport layer (with TLS) to `intake.sekoia.io:50514`.
+
+For security reason, you may require to secure the collect of events between our equipments/sources and the syslog forwarder.
+
+## Generate the certificates
+
+### Install OpenSSL
+
+According to your operating system, install `openssl` to generate the certificates.
+
+On Debian-like distributions:
+```
+$ sudo apt install openssl
+```
+
+On Redhat-like distributions:
+```
+$ sudo dnf install openssl
+```
+
+On Mac OS X (with homebrew):
+```
+$ sudo brew install openssl
+```
+
+### Generate the Certificate Autority (CA)
+
+Create a directory that will contain your certificates.
+Open a terminal and type:
+
+```
+$ mkdir mycertificates && cd mycertificates
+```
+
+#### Generate the private key
+
+In the terminal, create the private key of the CA.
+
+```
+$ certtool --generate-privkey --outfile ca-key.pem --sec-param High
+Generating a 3072 bit RSA private key…
+```
+
+#### Generate the CA certificate
+
+In the terminal, generate the certificate of the CA. Type the name of the authority, define the expiration time and set this certificate as an authority certificate.
+
+```
+# Generate the CA certificate
+$ certtool --generate-self-signed --load-privkey ca-key.pem --outfile ca.pem
+Generating a self signed certificate...
+Please enter the details of the certificate's distinguished name. Just press enter to ignore a field.
+Common name: logconcentrator.domain.tld
+[...]
+The certificate will expire in (days): 3650
+ 
+Extensions.
+Does the certificate belong to an authority? (y/N): y
+[...]
+Will the certificate be used to sign other certificates? (y/N): y
+[...]
+Is the above information ok? (y/N): y
+ 
+Signing certificate…
+
+# Change the permission, on the certificate, to read-only
+$ chmod 600 ca.pem
+```
+
+Copy this certificate on your equipments/sources, in the registry/directory for Certificate Authority
+
+### Generate the certificate
+
+To secure the incoming events to the syslog forwarder, generate a server certificate.
+
+
+#### Generate the private key
+
+In the terminal, create the private key.
+
+```
+# Generate the server key
+$ certtool --generate-privkey --outfile server.pem --sec-param High
+Generating a 3072 bit RSA private key…
+
+# Change the permission, on the key, to read-only
+$ chmod 600 server.pem
+```
+
+#### Generate the Certificate Signing Request (CSR)
+
+In the terminal, generate the CSR:
+
+```
+$ certtool --generate-request --load-privkey server.pem --outfile server.csr
+Generating a PKCS #10 certificate request...
+Common name: logserveur.test.local
+[...]
+Enter a dnsName of the subject of the certificate: logconcentrator.domain.tld
+[...]
+Is this a TLS web client certificate? (y/N): y
+Is this a TLS web server certificate? (y/N): y
+```
+
+#### Generate the certificate for the syslog forwarder
+
+In the terminal, generate the certificate of the syslog forwarder. Define the certificate as a server certificate and type the domain name of the syslog forwarder.
+
+```
+# Generate the server certificate
+$ certtool --generate-certificate --load-request server.csr --outfile server.crt --load-ca-certificate ca.pem --load-ca-privkey ca-key.pem
+Generating a signed certificate...
+[...]
+Activation/Expiration time.
+The certificate will expire in (days): 365
+ 
+ 
+Extensions.
+Does the certificate belong to an authority? (y/N): n
+Is this a TLS web client certificate? (y/N): n
+Is this a TLS web server certificate? (y/N): y
+Enter a dnsName of the subject of the certificate: logconcentrator.domain.tld
+[...]
+Is the above information ok? (y/N): y
+ 
+Signing certificate…
+
+# Change the permission, on the certificate, to read-only
+$ chmod 600 server.crt
+```
+
+## Secure the collect of events with stunnel
+
+### Install stunnel
+
+According to your operating system, install `stunnel`.
+
+On Debian-like distributions:
+```
+$ sudo apt install stunnel
+```
+
+On Redhat-like distributions:
+```
+$ sudo dnf install stunnel
+```
+
+### Move the certificates
+
+```
+# Create the directory for certificates
+$ mkdir -p /etc/stunnel/certificates/
+
+# Copy the certificates
+$ cp ca.pem server.pem server.crt /etc/stunnel/certificates/
+```
+
+### Configure stunnel
+
+Configure stunnel to accept secured connection and forward the events to the syslog forwarder:
+
+```
+# Create the configuration if not exist
+$ sudo touch /etc/stunnel/default.conf
+
+# Set the configuration
+$ sudo vi /etc/stunnel/default.conf
+; It is recommended to drop root privileges if stunnel is started by root
+setuid = stunnel4
+setgid = stunnel4
+
+; PID file is created inside the chroot jail (if enabled)
+pid = /var/run/stunnel4/stunnel.pid
+
+output = /var/log/stunnel4/stunnel.log
+
+[secured_source_tunnel]
+client = no
+accept = 6514
+connect = <address of the syslog forwarder>:<port to forward to>
+cert = /etc/stunnel/certificates/server.crt
+key = /etc/stunnel/certificates/server.pem
+CAfile = /etc/stunnel/certificates/ca.pem
+```
+
+### Start stunnel
+
+In the terminal, start stunnel:
+
+```
+$ sudo stunnel /etc/stunnel/default.conf
+```