openssl config file for a root CA that will sign requests with subjectAltName(s)

rootCA.cfg

#
# OpenSSL example configuration file.
# This is mostly being used for generation of certificate requests.
#

# This definition stops the following lines choking if HOME isn't
# defined.
HOME			= .
RANDFILE		= $ENV::HOME/.rnd

# Extra OBJECT IDENTIFIER info:
#oid_file		= $ENV::HOME/.oid
oid_section		= new_oids

[ new_oids ]

# We can add new OIDs in here for use by 'ca' and 'req'.
# Add a simple OID like this:
# testoid1=1.2.3.4
# Or use config file substitution like this:
# testoid2=${testoid1}.5.6

####################################################################
[ ca ]
default_ca	= CA_default		# The default ca section

####################################################################
[ CA_default ]

dir		          = /usr/local/rootCA
certs		        = $dir/certs
crl_dir		      = $dir/crl
database	      = $dir/index.txt
unique_subject	= no
new_certs_dir	  = $dir/new_certs
certificate	    = $dir/rootCA.cert
serial		      = $dir/serial
crlnumber	      = $dir/crlnumber
crl		          = $dir/crl.pem
private_key	    = $dir/rootCA.key
RANDFILE      	= $dir/private/.rand

x509_extensions	= usr_cert

name_opt 	= ca_default		# Subject Name options
cert_opt 	= ca_default		# Certificate field options

copy_extensions = copy

default_days	   = 3650
default_crl_days = 365
default_md	     = sha256
preserve	       = no

policy		= policy_anything

[ policy_anything ]
countryName		         = optional
stateOrProvinceName	   = optional
localityName		       = optional
organizationName	     = optional
organizationalUnitName = optional
commonName		         = supplied
emailAddress		       = optional

####################################################################
[ req ]
default_bits		   = 2048
default_keyfile 	 = rootCA.key
distinguished_name = req_distinguished_name
attributes		     = req_attributes
x509_extensions	   = v3_ca	# The extentions to add to the self signed cert
encrypt_key		     = no

string_mask = nombstr

[ req_distinguished_name ]
countryName			    = Country Name (2 letter code)
countryName_default	= AU
countryName_min			= 2
countryName_max			= 2

stateOrProvinceName		      = State or Province Name (full name)
stateOrProvinceName_default	= NSW

localityName			   = Locality Name (eg, city)
localityName_default = Sydney

0.organizationName		     = Organization Name (eg, company)
0.organizationName_default = Pivotal

organizationalUnitName		= Organizational Unit Name (eg, section)
#organizationalUnitName_default	=

commonName		 = Common Name (e.g. server FQDN or YOUR name)
commonName_max = 64

emailAddress     = Email Address
emailAddress_max = 64


[ req_attributes ]
challengePassword		  = A challenge password
challengePassword_min	= 4
challengePassword_max	= 20

unstructuredName		= An optional company name

[ usr_cert ]

# These extensions are added when 'ca' signs a request.

basicConstraints=CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer

[ v3_req ]

# Extensions to add to a certificate request

basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment

[ v3_ca ]

# Extensions for a typical CA

subjectKeyIdentifier=hash

authorityKeyIdentifier=keyid:always,issuer:always

basicConstraints = CA:true


[ crl_ext ]

# CRL extensions.
# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always,issuer:always

[ proxy_cert_ext ]
# These extensions should be added when creating a proxy certificate

basicConstraints=CA:FALSE

nsComment			= "OpenSSL Generated Certificate"

subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer:always

proxyCertInfo=critical,language:id-ppl-anyLanguage,pathlen:3,policy:foo

generate a key and cert for the rootCA itself:
openssl req -new -x509 -keyout rootCA.key -out rootCA.cert -config rootCA.cfg -days 3650

create starting files
mkdir new_certs
touch index.txt
openssl rand -hex 16 > serial

You're now ready to issue certs.

To issue a cert from a request (see https://gist.github.com/sturadnidge/c6351940d84896107608e41f5417f20a for how to generate certificate requests)
openssl ca -in A_CERT_REQUEST.csr -out A_CERT.cert -config /path/to/rootCA.cfg