Generating a CSR with Python (crypto)

Question

I have a skeleton that -- works, but I'm kind of stuck on the following;

1. I don't see a way with the crypto library to handle SAN (subjectAltName)? Hopefully I'm not wrong on the terminology, but if I have say -- one main hostname test.test.edu and then alternatively would like that host to also be pushu.edu, usually that can be a "subjectAltName".
2. Is there any way to see the entire CSR? Like, where it shows the Subject, State, etc, etc? I just want to see it printed to screen, but I don't see a way to do this with crypto.

Any help would be greatly appreciated; code thus far -

#!/usr/bin/env python

from OpenSSL import crypto, SSL
import subprocess, os, sys

# Create 'usage' portion
# Something, blah blah, use script like this, blah blah.

# Variable
TYPE_RSA = crypto.TYPE_RSA

# Generate pkey
def generateKey(type, bits):

    keyfile = 'incommon.key'
    key = crypto.PKey()
    key.generate_key(type, bits)
    if os.path.exists(keyfile):
        print "Certificate file exists, aborting."
        print " ", keyfile
        sys.exit(1)
    else:
        f = open(keyfile, "w")
        f.write(crypto.dump_privatekey(crypto.FILETYPE_PEM, key))
        f.close()
    return key

# Generate CSR
def generateCSR(nodename):

    csrfile = 'incommon.csr'
    req = crypto.X509Req()
    # Return an X509Name object representing the subject of the certificate.
    req.get_subject().CN = nodename
    #req.get_subject().countryName = 'xxx'
    #req.get_subject().stateOrProvinceName = 'xxx'
    #req.get_subject().localityName = 'xxx'
    #req.get_subject().organizationName = 'xxx'
    #req.get_subject().organizationalUnitName = 'xxx'
    # Set the public key of the certificate to pkey.
    req.set_pubkey(key)
    # Sign the certificate, using the key pkey and the message digest algorithm identified by the string digest.
    req.sign(key, "sha1")
    # Dump the certificate request req into a buffer string encoded with the type type.
    if os.path.exists(csrfile):
        print "Certificate file exists, aborting."
        print " ", csrfile
        sys.exit(1)
    else:
        f = open('incommon.csr', "w")
        f.write(crypto.dump_certificate_request(crypto.FILETYPE_PEM, req))
        f.close()

#Call key & CSR functions
key = generateKey(TYPE_RSA,2048)
# Needs to take input from user.
generateCSR('test.test.edu')

EDIT:

I ended up fixing this awhile ago. Here's the code with the added extensions, or you can clone it from my Github: https://github.com/cjcotton/python-csr;

# Generate Certificate Signing Request (CSR)
def generateCSR(nodename, sans = []):

    C  = raw_input('Enter your country: ')
    ST = raw_input("Enter your state: ")
    L  = raw_input("Enter your location: ")
    O  = raw_input("Enter your organization: ")
    OU = raw_input("Enter your organizational unit: ")

    # Allows you to permanently set values required for CSR
    # To use, comment raw_input and uncomment this section.
    # C  = 'US'
    # ST = 'New York'
    # L  = 'Location'
    # O  = 'Organization'
    # OU = 'Organizational Unit'

    csrfile = 'host.csr'
    keyfile = 'host.key'
    TYPE_RSA = crypto.TYPE_RSA
    # Appends SAN to have 'DNS:'
    ss = []
    for i in sans:
        ss.append("DNS: %s" % i)
    ss = ", ".join(ss)

    req = crypto.X509Req()
    req.get_subject().CN = nodename
    req.get_subject().countryName = C
    req.get_subject().stateOrProvinceName = ST
    req.get_subject().localityName = L
    req.get_subject().organizationName = O
    req.get_subject().organizationalUnitName = OU
    # Add in extensions
    base_constraints = ([
        crypto.X509Extension("keyUsage", False, "Digital Signature, Non Repudiation, Key Encipherment"),
        crypto.X509Extension("basicConstraints", False, "CA:FALSE"),
    ])
    x509_extensions = base_constraints
    # If there are SAN entries, append the base_constraints to include them.
    if ss:
        san_constraint = crypto.X509Extension("subjectAltName", False, ss)
        x509_extensions.append(san_constraint)
    req.add_extensions(x509_extensions)
    # Utilizes generateKey function to kick off key generation.
    key = generateKey(TYPE_RSA, 2048)
    req.set_pubkey(key)
    req.sign(key, "sha1")
    generateFiles(csrfile, req)
    generateFiles(keyfile, key)
    return req

Answer 1

For your first question about how to add a SAN to a CSR, look into using the add_extensions method on the X509req object (which is curiously not mentioned in the docs for the X509req class)

It would look something like this

altnames = ', '.join(['DNS:foo.example.com',
                      'DNS:bar.example.com', 
                      'IP:203.0.113.12'])
req.add_extensions([OpenSSL.crypto.X509Extension("subjectAltName", 
                                                 False, 
                                                 altnames)])

Update : Thanks to Peter Gallagher for catching the missing type prefixes (e.g. DNS, IP) in my original answer.

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