Sample OpenSSL configuration for local CA; see my CA guide: https://github.com/messa/tips/blob/master/OpenSSL.md

openssl.conf

[ ca ]
default_ca = CA_default

[ CA_default ]
dir               = /XXX/root-ca
certs             = $dir/certs
crl_dir           = $dir/crl
new_certs_dir     = $dir/newcerts
database          = $dir/index.txt
serial            = $dir/serial
RANDFILE          = $dir/private/.rand

# The root key and root certificate.
private_key       = $dir/private/ca.key.pem
certificate       = $dir/certs/ca.cert.pem

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/ca.crl.pem
crl_extensions    = crl_ext
default_crl_days  = 30

default_md        = sha256

name_opt          = ca_default
cert_opt          = ca_default
default_days      = 36500
preserve          = no
policy            = policy_strict

[ policy_strict ]
# This policy will be used for root CA, which should only sign intermediate certificates that match.
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ policy_loose ]
# Allow the intermediate CA to sign a more diverse range of certificates.
# See the POLICY FORMAT section of the `ca` man page.
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional
DC                      = optional

[ req ]
default_bits        = 4096
distinguished_name  = req_distinguished_name
string_mask         = utf8only

default_md          = sha256

# Extension to add when the -x509 option is used.
x509_extensions     = v3_ca

[ req_distinguished_name ]
# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
0.DC                            = Domain Component
commonName                      = Common Name
emailAddress                    = Email Address

# The Domain Component (DC) is useful for distinguishing between cluster and
# client certificates in MongoDB SSL deployments.

# Optionally, specify some defaults.
countryName_default             = GB
stateOrProvinceName_default     = England
localityName_default            =
0.organizationName_default      = Alice Ltd
organizationalUnitName_default  =
0.DC_default                    =
emailAddress_default            =

[ v3_ca ]
# Extensions for a typical CA (man x509v3_config).
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid:always,issuer
basicConstraints        = critical, CA:true
keyUsage                = critical, digitalSignature, cRLSign, keyCertSign

[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (man x509v3_config).
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid:always,issuer
basicConstraints        = critical, CA:true, pathlen:0
keyUsage                = critical, digitalSignature, cRLSign, keyCertSign

[ usr_cert ]
# Extensions for client certificates (man x509v3_config).
basicConstraints        = CA:FALSE
nsCertType              = client, email
nsComment               = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid,issuer
keyUsage                = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage        = clientAuth, emailProtection

[ server_cert ]
# Extensions for server certificates (man x509v3_config).
basicConstraints        = CA:FALSE
nsCertType              = server
nsComment               = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid,issuer:always
keyUsage                = critical, digitalSignature, keyEncipherment
extendedKeyUsage        = serverAuth

[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier = keyid:always

[ ocsp ]
# Extension for OCSP signing certificates (man ocsp).
basicConstraints        = CA:FALSE
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid,issuer
keyUsage                = critical, digitalSignature
extendedKeyUsage        = critical, OCSPSigning