1. 准备好目录
   
   serial文件中要填一个00进去
2. 生成 CA
   2.1 生成私钥

openssl ecparam -genkey -name secp256r1 |openssl ec -out private/ca.key.pem

2.2 使用 ECC 算法生成 256 位 CA 私钥 生成自签署证书，类型由

openssl.cnf 中配置的扩展字段指定为 CA 证书类型

openssl req -config openssl.cnf -key private/ca.key.pem -new -x509 -days 7300 -sha256 -extensions v3_ca -out certs/ca.cert.pem

需要输入各项信息。由于是 CA 根证书， Common Name 字段不需要为域名。这里使用的 localhost
生成后即可将 certs/ca.cert.pem 安装于客户端操作系统/浏览器中作为受信任的跟证书颁发机构，由此 CA 签署的证书均会被客户端信任

3. 生成服务器密钥
   3.1 生成私钥

openssl ecparam -genkey -name secp256r1 | openssl ec -out private/stf.key.pem

 与 CA 私钥生成方法相同
 生成证书请求文件

openssl req -config openssl.cnf -new -key private/stf.key.pem -out certs/stf.csr.pem

填写证书相关信息，这里 Common Name 字段需要为证书域名。需要提前在 openssl.cnf 中编辑好 subjectAltName 以保证证书扩展字段中 DNS 可选域名正确。

3.2 使用 CA 签发服务器证书

openssl ca -config openssl.cnf -extensions server_cert -days 1095 -md sha256 -in certs/stf.csr.pem -out certs/stf.cert.pem

需要提前在 openssl.cnf 中编辑好 subjectAltName 以保证证书扩展字段中 DNS 可选域名正确。

4. 使用 openssl 生成带有 SAN 扩展的证书请求文件（CSR）
   4.1 找到 [ req ] 段落，加上下面的配置

req_extetions = v3_req

这段配置表示在生成 CSR 文件时读取名叫 v3_req 的段落的配置信息，因此我们再在此配置文件中加入一段名为 v3_req 的配置：

[ v3_req ]
# Extensions to add to a certificate request

basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names

这段配置中最重要的是在最后导入名为 alt_names 的配置段，因此我们还需要添加一个名为 [ alt_names ] 的配置段：

[ alt_names ]
DNS.1 = www.ustack.in
DNS.2 = www.test.ustack.com

这里填入需要加入到 Subject Alternative Names 段落中的域名名称，可以写入多个。
接着使用这个临时配置生成证书：

openssl req -new -nodes -keyout ustack.key -out ustack.csr -config ./ca/openssl.cnf

查看证书请求文件的内容：

openssl req -text -noout -in ustack.csr

可以看到此证书请求文件中会包含 Subject Alternative Names 字段，并包含之前在配置文件中填写的域名。

5. 使用 openssl 签署带有 SAN 扩展的证书请求
   5.1 假设使用本机作为子签署 CA 对此证书请求进行签署，签署的方式为：

openssl ca -policy policy_anything -out ustack.crt -config ./ca/openssl.cnf -extensions v3_req -infiles ustack.csr

签署后，查看证书的内容：

openssl x509 -text -noout -in ustack.crt

附上openssl.cfg

[ ca ]
# `man ca`
default_ca = CA_default

[ CA_default ]
# Directory and file locations.
dir               = ./ca#这里改成实际目录
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

# SHA-1 is deprecated, so use SHA-2 instead.
default_md        = sha256

name_opt          = ca_default
cert_opt          = ca_default
default_days      = 375
preserve          = no
policy            = policy_strict

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ policy_anything ]
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
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

[ req ]
# Options for the `req` tool (`man req`).
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

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

req_extensions = v3_req

[ 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
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = CN
stateOrProvinceName_default     = China
localityName_default            =
0.organizationName_default      = zhihu
#organizationalUnitName_default =
#emailAddress_default           =

[ v3_req ]

# Extensions to add to a certificate request

basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = zhihu.com
DNS.2 = *.zhihu.com
DNS.3 = localhost

[ 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
subjectAltName = @alt_names

[ 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

以上大部分内容来自网上，其中根据自身情况做了调整
https://liaoph.com/openssl-san/
https://zhuanlan.zhihu.com/p/34788439