@deftypefun {int} {gnutls_reauth} (gnutls_session_t @var{session}, unsigned int @var{flags})

@var{session}: is a @code{gnutls_session_t}  type.

@var{flags}: must be zero

This function performs the post-handshake authentication

for TLS 1.3. The post-handshake authentication is initiated by the server

by calling this function. Clients respond when @code{GNUTLS_E_REAUTH_REQUEST} 

has been seen while receiving data.

The non-fatal errors expected by this function are:

@code{GNUTLS_E_INTERRUPTED} , @code{GNUTLS_E_AGAIN} , as well as

@code{GNUTLS_E_GOT_APPLICATION_DATA}  when called on server side.

The former two interrupt the authentication procedure due to the transport

layer being interrupted, and the latter because there were pending data prior

to peer initiating the re-authentication. The server should read/process that

data as unauthenticated and retry calling @code{gnutls_reauth()} .

When this function is called under TLS1.2 or earlier or the peer didn't

advertise post-handshake auth, it always fails with

@code{GNUTLS_E_INVALID_REQUEST} . The verification of the received peers certificate

is delegated to the session or credentials verification callbacks. A

server can check whether post handshake authentication is supported

by the client by checking the session flags with @code{gnutls_session_get_flags()} .

Prior to calling this function in server side, the function

@code{gnutls_certificate_server_set_request()}  must be called setting expectations

for the received certificate (request or require). If none are set

this function will return with @code{GNUTLS_E_INVALID_REQUEST} .

Note that post handshake authentication is available irrespective

of the initial negotiation type (PSK or certificate). In all cases

however, certificate credentials must be set to the session prior

to calling this function.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on a successful authentication, otherwise a negative error code.

@end deftypefun