This implement a large majority of OpenSSL's useful X509 API.

  The email() method supports both certificates where the
  subject is of the form:
  "... CN=Firstname lastname/emailAddress=user@domain", and also
  certificates where there is a X509v3 Extension of the form
  "X509v3 Subject Alternative Name: email=user@domain".

WWW: https://metacpan.org/release/Crypt-OpenSSL-X509