Copy the default template of openssl.cnf to a writable location.
cp /System/Library/OpenSSL/openssl.cnf src
Uncomment the req_extensions = v3_req
req_extensions = v3_req # The extensions to add to a certificate request
Add subjectAltName to v3_req section
[ v3_req ]
# Extensions to add to a certificate request
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names
Add the main hostname and the wildcard to a new [alt_names] section
[alt_names]
DNS.1 = yourdomain.com
DNS.2 = *.yourdomain.com
For example, for mydomain.com
[alt_names]
DNS.1 = mydomain.com
DNS.2 = *.mydomain.com
Run the following and fill all the essential information, especially the CN (Common Name):
openssl genrsa -des3 -out hostname.key 2048
openssl rsa -in hostname.key -out hostname-key.pem
openssl req -new -key hostname-key.pem -out hostname-request.csr
openssl x509 -req -extensions v3_req -days 365 -in hostname-request.csr -signkey hostname-key.pem -out hostname-cert.pe