docs: def get_subjects(request):
      """Get all subjects in the certificate.
  
      - Returns: primary_str (primary subject), equivalent_set (equivalent identities,
        groups and group memberships)
      - The primary subject is the certificate subject DN, serialized to a DataONE
        compliant subject string.
  
      """
      if _is_certificate_provided(request):
          try:
              return get_authenticated_subjects(request.META['SSL_CLIENT_CERT'])
          except Exception as e:
              raise d1_common.types.exceptions.InvalidToken(
                  0,
                  'Error extracting session from certificate. error="{}"'.format(str(e)),
              )
      else:
          return d1_common.const.SUBJECT_PUBLIC, set()