OpenSSL子CA签发含SAN字段的网站证书失败问题咨询

原环境基于Microsoft Certificate Authority搭建PKI架构：根CA脱离域并处于关机状态，子CA加入域，通过IIS提供CRL服务并为域内计算机签发证书。现计划通过Linux+OpenSSL复刻该环境，核心目标是为内部网站签发证书。

目前已完成自签名根CA、根CA签发的子CA的创建，证书链验证正常，但在签发带**Subject Alternative Name（SAN）**字段的网站证书时遇到问题：

1. 使用以下命令生成的CSR中包含正确的SAN字段：

openssl req -nodes -new -newkey rsa:4096 \
    -keyout test3.psc.local.key \
    -out test3.psc.local.csr \
    -addext "subjectAltName = DNS:test3.psc.local" \
    -subj "/C=ES/ST=Barcelona/L=Barcelona/O=GRG-CA/OU=GRG-CA/emailAddress=your@email.dot/CN=test3.psc.local/"

通过openssl x509 -noout -text -in test3.psc.local.csr检查，确认SAN字段存在且值正确。

2. 使用子CA签发证书后，生成的证书缺失SAN字段，导致Chrome、Firefox等主流浏览器不信任该证书，仅IE11可正常识别：

openssl ca -config intermediate/sub-ca-openssl.cnf \
    -extensions server_cert    \
    -days 375 -notext -md sha512     \
    -in /root/ca/test3.psc.local.csr     \
    -out /root/ca/test3.psc.local.crt

子CA配置文件内容如下：

[ ca ]
default_ca = CA_default

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

private_key       = $dir/private/intermediate.key.pem
certificate       = $dir/certs/intermediate.cert.pem

crlnumber         = $dir/crlnumber
crl               = $dir/crl/intermediate.crl.pem
crl_extensions    = crl_ext
default_crl_days  = 365

default_md        = sha512

name_opt          = ca_default
cert_opt          = ca_default

default_days      = 5840
preserve          = no
policy            = subca_policy

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

[ req ]
default_bits        = 4096
distinguished_name  = req_distinguished_name
string_mask         = utf8only
default_md          = sha512
x509_extensions     = v3_ca

[ req_distinguished_name ]
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             = ES
stateOrProvinceName_default     = Barcelona
localityName_default            = Barcelona
0.organizationName_default      = GRG-CA
organizationalUnitName_default  = GRG-CA
#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
crlDistributionPoints = URI:http://pki.dominio.com/intermediate.crl

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

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

[ crl_info ]
URI.0 = http://pki.dominio.com/sub-ca.crl
URI.1 = https://www.dominio.com/pki/sub-ca.crl 

希望实现类似Microsoft SubCA的效果：仅在生成CSR时指定SAN，签发时无需修改CA配置。

要让OpenSSL子CA自动读取CSR中的SAN字段并写入签发的证书，只需修改子CA配置文件的两个核心设置：

1. 启用扩展字段复制 #

在[CA_default]段中添加以下配置：

copy_extensions = copy

该参数会让OpenSSL将CSR中包含的所有扩展字段（包括SAN）直接复制到最终签发的证书中，无需在CA配置里预先定义SAN值。

2. 确保server_cert扩展兼容 #

检查[server_cert]段，确保没有定义subjectAltName字段（如果已定义，会覆盖CSR中的值）。当前配置中的server_cert段未包含该字段，无需额外修改。

3. 重新签发证书 #

使用原有的签发命令重新生成证书即可：

openssl ca -config intermediate/sub-ca-openssl.cnf \
    -extensions server_cert    \
    -days 375 -notext -md sha512     \
    -in /root/ca/test3.psc.local.csr     \
    -out /root/ca/test3.psc.local.crt

4. 验证结果 #

执行以下命令确认证书中已包含SAN字段：

openssl x509 -noout -text -in test3.psc.local.crt | grep -A 3 "Subject Alternative Name"

注意事项 #

• copy_extensions = copy会复制CSR中的所有扩展字段，需确保提交的CSR扩展合规，避免签发不符合安全要求的证书。若需更精细控制，可使用copy_extensions = copyall（但需谨慎，会复制所有扩展，包括可能的敏感字段）。
• 确保子CA配置文件的权限正确（建议设置为600，仅CA管理员可读写），避免配置被篡改。

内容的提问来源于stack exchange，提问作者Guille