Using the following functions, you can attach arbitrary notation data to a signature. This information is then available to the user when the signature is verified.
gpgme_sig_notation_clear removes the notation data
from the context ctx. Subsequent signing operations from this
context will not include any notation data.
Every context starts with an empty notation data list.
gpgme_sig_notation_add adds the notation data with
the name name and the value value to the context
Subsequent signing operations will include this notation data, as well
as any other notation data that was added since the creation of the
context or the last
The arguments name and value must be
strings in human-readable form. The flag
GPGME_SIG_NOTATION_HUMAN_READABLE is implied
(non-human-readable notation data is currently not supported). The
strings must be in UTF-8 encoding.
If name is
NULL, then value should be a policy URL.
gpgme_sig_notation_add returns the error code
GPG_ERR_NO_ERROR if the notation data could be added
GPG_ERR_INV_VALUE if ctx is not a valid
pointer, or if name, value and flags are an invalid
combination. The function also passes through any errors that are
reported by the crypto engine support routines.
gpgme_sig_notation_get returns the linked list of
notation data structures that are contained in the context ctx.
If ctx is not a valid pointer, or there is no notation data
added for this context,
NULL is returned.