Look up the issuer of
certificate in the database.
The issuer property of
certificate is not modified, and
the two certificates are not hooked into a chain.
This function can block. Use lookup_certificate_issuer_async to perform the lookup operation asynchronously.
Beware this function cannot be used to build certification paths. The issuer certificate returned by this function may not be the same as the certificate that would actually be used to construct a valid certification path during certificate verification. RFC 4158 explains why an issuer certificate cannot be naively assumed to be part of the the certification path (though GLib's TLS backends may not follow the path building strategies outlined in this RFC). Due to the complexity of certification path building, GLib does not provide any way to know which certification path will actually be used when verifying a TLS certificate. Accordingly, this function cannot be used to make security-related decisions. Only GLib itself should make security decisions about TLS certificates.
used to interact with the user if necessary
flags which affect the lookup operation
a Cancellable, or null