@deftypefun {int} {gnutls_register_custom_url} (const gnutls_custom_url_st * @var{st})
@var{st}: A @code{gnutls_custom_url_st}  structure

Register a custom URL. This will affect the following functions:
@code{gnutls_url_is_supported()} , @code{gnutls_privkey_import_url()} ,
gnutls_pubkey_import_url, @code{gnutls_x509_crt_import_url()}  
and all functions that depend on
them, e.g., @code{gnutls_certificate_set_x509_key_file2()} .

The provided structure and callback functions must be valid throughout
the lifetime of the process. The registration of an existing URL type
will fail with @code{GNUTLS_E_INVALID_REQUEST} . Since GnuTLS 3.5.0 this function
can be used to override the builtin URLs.

This function is not thread safe.

@strong{Returns:} returns zero if the given structure was imported or a negative value otherwise.

@strong{Since:} 3.4.0
@end deftypefun