PKI: T6259: Support RFC822 names in certificate generation

[Embezzle]

Change Summary

Add the ability to specific RFC822 (email) names as Subject Alternative Names in x509 certificates generated via the PKI system.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

https://vyos.dev/T6259

Related PR(s)

Component(s) name

PKI

Proposed changes

How to test

1. Generate a new certificate using the PKI system that contains an RFC822 SAN:

vyos@vyos:~$ generate pki certificate self-signed file test-t6259
Enter private key type: [rsa, dsa, ec] (Default: rsa) rsa
Enter private key bits: (Default: 2048) 2048
Enter country code: (Default: GB) GB
Enter state: (Default: Some-State) Some-State
Enter locality: (Default: Some-City) Some-City
Enter organization name: (Default: VyOS) VyOS
Enter common name: (Default: vyos.io) vyos.net
Do you want to configure Subject Alternative Names? [y/N] y
Enter alternative names in a comma separate list, example: ipv4:1.1.1.1,ipv6:fe80::1,dns:vyos.net,rfc822:user@vyos.net
Enter Subject Alternative Names: dns:vyos.net,rfc822:exampleuser@vyos.net
Enter how many days certificate will be valid: (Default: 365) 365
Enter certificate type: (client, server) (Default: server) server
Note: If you plan to use the generated key on this router, do not encrypt the private key.
Do you want to encrypt the private key with a passphrase? [y/N] n
File written to /config/auth/test-t6259.pem
File written to /config/auth/test-t6259.key

2. Validate that the SAN extension contains the requested names:

vyos@vyos:~$ openssl x509 -inform pem -noout -text -in "/config/auth/test-t6259.pem" | grep "Subject Alternative Name" -A 1
            X509v3 Subject Alternative Name:
                DNS:vyos.net, email:exampleuser@vyos.net

Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[c-po]

Please give the documentation an update, too. Other then that LGTM