Generate self signed certificates

Self-signed certificates can be generated using tools, such as openssl.

For example:

$ openssl req -newkey rsa:2048 -nodes -keyout key.pem -x509 -days 365 -out certificate.pem
Generating a RSA private key
...................................
writing new private key to 'key.pem'
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You are about to be asked to enter information that will be incorporated into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
. . .
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Country Name (2 letter code) [XX]:Your country code
State or Province Name (full name) []:Your state
Locality Name (eg, city) [Default City]:Your City
Organization Name (eg, company) [Default Company Ltd]:Your Company, Inc
Organizational Unit Name (eg, section) []:Your organinzational unit. 
Common Name (eg, your name or your server's hostname) []:*.gateway.info
Email Address []:noreply@gateway.infp
$ ls *.pem
key.pem certificate.pem

See https://www.openssl.org/ for more information on Open SSL.