Use accessors for ASN1_STRING values

[bob-beck]

OpenSSL is going to make ASN1_STRING opaque. The accessors in question have been around in OpenSSL for a very long time.

see openssl/openssl#29117
and specifically openssl/openssl#29862

Description

Checklist

• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• This feature/change has adequate documentation added
• Code conform to coding style that today cannot yet be enforced via the check style test
• Commits have short titles and sensible commit messages
• Coverity Scan has run if needed (code PR) and no new defects were found

[simo5]

almost there :)

[simo5]

LGTM,
please squash the fixups and add your sign-off to the commit

[simo5]

Covscan servers are down for maintenance, will re-run the scan later, after squash and signoff are applied

[bob-beck]

LGTM

[simo5]

Unfortunately it seems coverity is having some extended maintenance issues, I can waive it off, but the DCO check is required. @bob-beck can you please ass the sign-off-by trailer to your commit ? (git commit -s --amend)