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Generate ssl certificates with Subject Alt Names

Generate ssl certificates with Subject Alt Names on OSX

Open ssl.conf in a text editor.

Edit the domain(s) listed under the [alt_names] section so that they match the local domain name you want to use for your project, e.g.

DNS.1   = my-project.dev

Additional FQDNs can be added if required:

DNS.1   = my-project.dev
DNS.2   = www.my-project.dev
DNS.3   = fr.my-project.dev

Create a directory for your project, e.g. my_project and save ssl.conf inside it.

Open Terminal and navigate to 'my_project':

cd my_project

Generate a private key:

openssl genrsa -out private.key 4096

Generate a Certificate Signing Request

openssl req -new -sha256 \
    -out private.csr \
    -key private.key \
    -config ssl.conf 

(You will be asked a series of questions about your certificate. Answer however you like, but for 'Common name' enter the name of your project, e.g. my_project)

Now check the CSR:

openssl req -text -noout -in private.csr

You should see this:

X509v3 Subject Alternative Name: DNS:my-project.site and Signature Algorithm: sha256WithRSAEncryption

Generate the certificate

openssl x509 -req \
    -sha256 \
    -days 3650 \
    -in private.csr \
    -signkey private.key \
    -out private.crt \
    -extensions req_ext \
    -extfile ssl.conf

Add the certificate to keychain and trust it:

sudo security add-trusted-cert -d -r trustRoot -k /Library/Keychains/System.keychain private.crt

(Alternatively, double click on the certificate file private.crt to open Keychain Access. Your project name my_project will be listed under the login keychain. Double click it and select 'Always trust' under the 'Trust' section.)

If you are using MAMP Pro, add (or edit) a host with the server name you listed under the [alt_names] section of your ssl.conf. On the SSL tab select the Certificate file and Certificate key that you just generated.

Save changes and restart Apache.

[ req ]
default_bits = 4096
distinguished_name = req_distinguished_name
req_extensions = req_ext
[ req_distinguished_name ]
countryName = Country Name (2 letter code)
countryName_default = GB
stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = England
localityName = Locality Name (eg, city)
localityName_default = Brighton
organizationName = Organization Name (eg, company)
organizationName_default = Hallmarkdesign
commonName = Common Name (e.g. server FQDN or YOUR name)
commonName_max = 64
commonName_default = localhost
[ req_ext ]
subjectAltName = @alt_names
[alt_names]
DNS.1 = your-website.dev
DNS.2 = another-website.dev
@ddfault
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ddfault commented May 27, 2020

Thank you for this post!!!! But had to dig further to get all the functionality I wanted. Here's the ssl.conf I ended up with.

[req]
default_bits       = 4096
distinguished_name = req_distinguished_name
req_extensions     = req_ext

[req_distinguished_name]
countryName                 = Country Name (2 letter code)
countryName_default         = GB
stateOrProvinceName         = State or Province Name (full name)
stateOrProvinceName_default = England
localityName                = Locality Name (eg, city)
localityName_default        = Brighton
organizationName            = Organization Name (eg, company)
organizationName_default    = Hallmarkdesign
commonName                  = Common Name (e.g. server FQDN or YOUR name)
commonName_max              = 64
commonName_default          = localhost

[req_ext]
keyUsage = digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth, clientAuth
subjectAltName = @alt_names

[alt_names]
DNS.1   = domainexample.com
DNS.2   = sub.domainexample.com
IP.1    = 169.254.124.124

Here was my commandline
"openssl.exe" x509 -req -days 730 -in request.req -CA ca.crt -CAkey ca.key -set_serial 02 -extensions req_ext -extfile ssl.conf -out request.crt

This got me a cert with key usage, extended key usage, and the subject alternative names I was looking for!

These were the other pages that helped me.
http://apetec.com/support/GenerateSAN-CSR.htm
https://www.openssl.org/docs/manmaster/man5/x509v3_config.html

This extra stuff was all in the request, but was ignored and not added to the output cert. Not sure how to pull from the request, but hand coding into the ssl.conf got me the one-off certificate I needed with all the stuff.

@BullwinkleDev
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It works like magic!
Thank you so much!!!

@v-andrius
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one liner to generate self-signed certificate with subjectAltName for testing:

openssl req -new -newkey rsa:2048 -nodes \
  -subj "/C=GB/ST=England/L=Brighton/O=Example/CN=*.example.com/emailAddress=info@example.com" \
  -reqexts SAN \
  -config <(cat /etc/ssl/openssl.cnf \
        <(printf "\n[SAN]\nsubjectAltName=DNS:example.com,DNS:www.example.com")) \
  -keyout example_com.key \
  -x509 -days 3650 -extensions SAN -out example_com.crt

Verify certificate:

openssl x509 -in /tmp/example.com.crt -noout -text

@wiwan-wijoyo
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Thanks, it worked..

@kevinsulatra
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Thank you very much. It worked.

@masayyed
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masayyed commented Dec 22, 2021

Thanks Thanks a lot man.

@amcginlay
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Particular thanks for this bit.

openssl x509 -req \
    ...
    -extensions req_ext \
    -extfile ssl.conf

I looked far and wide for a way to transition usages from CSR to Certificate, and this was it.

@wibed
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wibed commented Aug 5, 2023

id like to chip in. found this one liner

openssl req \
  -x509 \
  -newkey rsa:4096 \
  -sha256 \
  -days 3560 \
  -nodes \
  -keyout tls.key 
  -out tls.crt \                  
  -subj '/CN=localhost' \
  -extensions san \
  -config <(cat << EOF
[req]
distinguished_name=req
[san]
subjectAltName=@alt_names
[alt_names]
DNS.1=localhost
EOF
)

im currently debugging so am not sure if this works, but i like the format

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