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I wish to configure OpenSSL such that when running openssl req -new to generate a new certificate signing request, I am prompted for any alternative subject names to include on the CSR.

I have added this line to the [req_attributes] section of my openssl.cnf:

subjectAltName                  = Alternative subject names

This has the desired effect that I am now prompted for SANs when generating a CSR:

$ openssl req -new -out test.csr -key ./test.key                            <<<
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [US]:
State or Province Name (full name) [New York]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Example Co]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:test.example.com
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
Alternative subject names []:DNS:alt1.example.com

In the above example, I have entered DNS:alt1.example.com when prompted for the SANs.

The problem is that the resulting CSR does not appear to be well formatted:

$ openssl req -text -in ./test.csr
Certificate Request:
    Data:
        Version: 0 (0x0)
        Subject: C=US, ST=New York, O=The Banes, CN=test.thebanes.org
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    [...]
                Exponent: 65537 (0x10001)
        Attributes:
            X509v3 Subject Alternative Name:unable to print attribute

OpenSSL complains that it is unable to print the value of the Subject Alternative Name attribute. From examples online (where people hard-code the SANs into their openssl.cnf, rather than prompting for them interactively as I want), I expect to see this instead:

        Attributes:
            X509v3 Subject Alternative Name:
                DNS:alt1.example.com

So, how can I generate a well-formed CSR with interactively prompted SANs?

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1 Answer 1

I've battled with this little nugget myself ... what a PITA!

My solution: I moved the all of openssl.cnf file into a Template Toolkit file leaving only the sans piece as the replacement piece, then wrapped a perl script around it.

The perl script prompts for the SANs entries, then inserts them into the template, saves the template to a temp file and then I call openssl req with the -config option pointed at the temp file. discard the temp file after the CSR is generated.

You also might want to look at: http://www.openssl.org/docs/apps/config.html

There are others who override $ENV just prior to execution and wrap the call to openssl req in perl or shell and accomplish the same thing in a slightly more efficient manner: http://blog.loftninjas.org/2008/11/11/configuring-ssl-requests-with-subjectaltname-with-openssl/

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