The authority information access extension indicates how to access CA
information for the issuer of the certificate.
The following paragraph is taken from RFC 2459 (Housley, et. al.), part 188.8.131.52:
«Each entry ... describes the
format and location of additional information about the CA who issued
the certificate in which this extension appears. The type and format
of the information is specified by the accessMethod field; the
accessLocation field specifies the location of the information. The
retrieval mechanism may be implied by the accessMethod or specified
This profile defines one OID for accessMethod. The id-ad-caIssuers
OID is used when the additional information lists CAs that have
issued certificates superior to the CA that issued the certificate
containing this extension. The referenced CA Issuers description is
intended to aid certificate users in the selection of a certification
path that terminates at a point trusted by the certificate user.
This extension may be included in
subject or CA certificates, and it MUST be non-critical.