Get the certificate's full User ID. If the certificate contains
more than one User ID with different validities, the User ID with
the highest validity is returned. If more than one User ID appears
in the certificate with the same (highest) validity, the first such
User ID will be returned.
Get the certificate's full User ID. If the certificate contains more than one User ID with different validities, the User ID with the highest validity is returned. If more than one User ID appears in the certificate with the same (highest) validity, the first such User ID will be returned.