Generate Multi Domain SSL Certificate by useing cert bot tool from Let's Encrypt.

 We are using cert bot tool to generate / create multi domain certificate from Let's Encrypt CA.

we are using following command 

create CSR config file to generate CSR:

Example of csr file is:

default_bits            = 2048  # RSA key size
encrypt_key             = no  # Protect private key
default_md              = sha256  # MD to use
utf8                    = yes  # Input is UTF-8
string_mask             = utf8only  # Emit UTF-8 strings
prompt                  = no  # Prompt for DN
distinguished_name      = server_dn  # DN template
req_extensions          = server_reqext  # Desired extensions

[ server_dn ]
countryName             = CountryName # ISO 3166
stateOrProvinceName     = StateName
localityName            = CityName
organizationName        = OrgName
organizationalUnitName  = UnitName
commonName              = domainname.tld  # Should match a SAN under alt_names

[ server_reqext ]
basicConstraints        = CA:FALSE
keyUsage                = critical,digitalSignature,keyEncipherment
extendedKeyUsage        = serverAuth
subjectKeyIdentifier    = hash
subjectAltName          = @alt_names

[alt_names]
DNS.1            = domainname.tld  #Example
DNS.2            = subdomain1.domainname.tld  #Example
DNS.3            = subdomain2.domainname.tld  #Example

openssl req -new -nodes -sha256 -out newcsr.csr -config cert.cfg -keyout private.key

certbot certonly --csr newcsr.csr --manual --preferred-challenges dns -d "domainname.tld" -d "subdomain1.domainname.tld" -d "subdomain2.domainname.tld" 

 

now your file is generated use it and place it properly.