Extend x.509 parsing to include machine-readable info about subjectAlternativeNames

[StephenWall]

This adds an additional array element to the output of openssl_x509_parse() that includes detailed info about the subjectAlternativeName extension in an easily machine parsable format.

Example:
If the contents of the extension appear as this in the current openssl_x509_parse() output (wrapped for readability):

Array
(
    [name] => ...
    ...
    [extensions] => Array
        (
            [subjectAltName] =>
                DNS:www.good.org,
                email:good@good.org,
                IP Address:192.168.0.1,
                othername:<unsupported>,
                othername:SmtpUTF8Mailbox:test@test.example.com,
                URI:sip:6000@192.168.0.1,
                DirName:/C=US/ST=CA/L=San Francisco/O=Example Company/OU=Example Company Unit/CN=Bob,
                Registered ID:1.2.3.4.5
        )
)

you would see a new top-level array element like this:

Array
(
    ...
    [subjectAlternativeName] => Array
        (
            [0] => Array
                (
                    [type] => DNS
                    [value] => www.good.org
                )

            [1] => Array
                (
                    [type] => email
                    [value] => good@good.org
                )

            [2] => Array
                (
                    [type] => IP Address
                    [value] => 192.168.0.1
                )

            [3] => Array
                (
                    [type] => othername
                    [value] => Array
                        (
                            [1.3.6.1.5.5.7.8.7] => foo@example.org
                        )
                )

            [4] => Array
                (
                    [type] => othername
                    [value] => Array
                        (
                            [1.3.6.1.5.5.7.8.9] => test@test.example.com
                        )
                )

            [5] => Array
                (
                    [type] => URI
                    [value] => sip:6000@192.168.0.1
                )

            [6] => Array
                (
                    [type] => DirName
                    [value] => Array
                        (
                            [2.5.4.6] => US
                            [2.5.4.8] => CA
                            [2.5.4.7] => San Francisco
                            [2.5.4.10] => Example Company
                            [2.5.4.11] => Example Company Unit
                            [2.5.4.3] => Bob
                        )

                )

            [7] => Array
                (
                    [type] => Registered ID
                    [value] => 1.2.3.4.5
                )

        )
)

[StephenWall]

This does not handle Multi-RDNs in the dirName field. I.e, things that appear as DirName:/CN=John Doe/OU=Testing+O=Example Org, Inc./C=US (note the +). It's my understanding they are not commonly used. I'd like to support them, but it's not straightforward, as you don't know you have a multi-RDN until you hit the second element in the multi-RDN. 🙄