An array of certificate chains whose root is self signed (ie a root issuer), and whose
final certificate is an issuer that we trust. The root of the certificate should be
first certificate in the chain. The string is a DER-encoded
certificate, which typically must be decoded using
MIME.decode_base64 or Tools.PEM.Msg first.
If this array is left empty, and the context is set to verify certificates,
a certificate chain must have a root that is self signed.