Where <em>direction</em> is Sent or Received, <em>version</em> is the
	  protocol version, <em>content_type</em> is the message content type,
	  and <em>data</em> is more info on the message from the <code>SSL_trace</code> API.
	</dd>
	<br>

	<dt>
	  <strong>session</strong> <em>channel session_id ticket lifetime</em>
	</dt>
	<dd>
	  This form of callback is invoked by the OpenSSL function
	  <code>SSL_CTX_sess_set_new_cb()</code>.
	  Where <em>session_id</em> is the current session identifier,
	  <em>ticket</em> is the session ticket info, and <em>lifetime</em>
	  is the the ticket lifetime in seconds.

	<br>
	<br>

	<dl>

	<dt>
	  <strong>alpn</strong> <em>channel protocol match</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked when the client ALPN
	  extension is received. If <em>match</em> is true, <em>protocol</em>
	  is the first <b>-alpn</b> specified protocol common to the both the
	  client and server. If not, the first client specified protocol is
	  used. Called after hello and ALPN callbacks.
	</dd>

	<br>

	<dt>
	  <strong>hello</strong> <em>channel servername</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked during client hello
	  message processing. It is used to select an appropriate certificate to
	  present, and make other configuration adjustments relevant to that
	  server name and its configuration. Called before SNI and ALPN callbacks.
	</dd>

	<br>

	<dt>
	  <strong>sni</strong> <em>channel servername</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked when the SNI extension
	  from the client is received. Where <em>servername</em> is the client
	  provided server name from the <b>-servername</b> option. This is
	  used when a server supports multiple names, so the right certificate
	  can be used. Called after hello callback but before ALPN callback.

    } else if (ssl == NULL) {
	return SSL_TLSEXT_ERR_NOACK;
    }

    /* Create command to eval */
    cmdPtr = Tcl_DuplicateObj(statePtr->callback);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("session", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(Tcl_GetChannelName(statePtr->self), -1));

    /* Session id */
    session_id = SSL_SESSION_get_id(session, &ulen);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewByteArrayObj(session_id, (int) ulen));

    /* Session ticket */
    SSL_SESSION_get0_ticket(session, &ticket, &len2);

    if (statePtr->vcmd == (Tcl_Obj*)NULL) {
	return res;
    }

    /* Create command to eval */
    cmdPtr = Tcl_DuplicateObj(statePtr->vcmd);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("alpn", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(Tcl_GetChannelName(statePtr->self), -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(*out, -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewBooleanObj(res == SSL_TLSEXT_ERR_OK));

    /* Eval callback command */
    Tcl_IncrRefCount(cmdPtr);
    if ((code = EvalCallback(interp, statePtr, cmdPtr)) > 1) {
	res = SSL_TLSEXT_ERR_NOACK;

    if (statePtr->vcmd == (Tcl_Obj*)NULL) {
	return SSL_TLSEXT_ERR_OK;
    }

    /* Create command to eval */
    cmdPtr = Tcl_DuplicateObj(statePtr->vcmd);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("sni", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(Tcl_GetChannelName(statePtr->self), -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(servername , -1));

    /* Eval callback command */
    Tcl_IncrRefCount(cmdPtr);
    if ((code = EvalCallback(interp, statePtr, cmdPtr)) > 1) {
	res = SSL_TLSEXT_ERR_ALERT_WARNING;
	*alert = SSL_AD_UNRECOGNIZED_NAME; /* Not supported by TLS 1.3 */

    }
    remaining = len;
    servername = (const char *)p;

    /* Create command to eval */
    cmdPtr = Tcl_DuplicateObj(statePtr->vcmd);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("hello", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(Tcl_GetChannelName(statePtr->self), -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(servername, (int) len));

    /* Eval callback command */
    Tcl_IncrRefCount(cmdPtr);
    if ((code = EvalCallback(interp, statePtr, cmdPtr)) > 1) {
	res = SSL_CLIENT_HELLO_RETRY;
	*alert = SSL_R_TLSV1_ALERT_USER_CANCELLED;

	"error" {
	    foreach {chan msg} $args break

	    log 0 "TLS/$chan: error: $msg"
	}
	"info" {
	    # poor man's lassign
	    foreach {chan major minor msg type} $args break

	    if {$msg != ""} {
		append state ": $msg"
	    }
	    # For tracing
	    upvar #0 tls::$chan cb
	    set cb($major) $minor

	    log 2 "TLS/$chan: $major/$minor: $state"
	}
	"message" {
	    # poor man's lassign
	    foreach {chan direction version content_type msg} $args break

	    log 0 "TLS/$chan: info: $direction $msg"
	}
	"session" {
	    foreach {chan session_id ticket lifetime} $args break

	    log 0 "TLS/$chan: session: lifetime $lifetime"
	}
	default	{
	    return -code error "bad option \"$option\":\
		    must be one of error, info, or session"
	}
    }
}

#
# Sample callback when return value is needed
#
proc tls::validate_command {option args} {
    variable debug

    #log 2 [concat $option $args]

    switch -- $option {
	"alpn" {
	    foreach {chan protocol match} $args break

	    log 0 "TLS/$chan: alpn: $protocol $match"
	}
	"hello" {
	    foreach {chan servername} $args break

	    log 0 "TLS/$chan: hello: $servername"
	}
	"sni" {
	    foreach {chan servername} $args break

	    log 0 "TLS/$chan: sni: $servername"
	}
	"verify" {
	    # poor man's lassign
	    foreach {chan depth cert rc err} $args break

	}
	if {$cb(handshake) == "done"} {
	    return 1
	}
    }
}

proc tls::password {rwflag size} {
    log 0 "TLS/Password: did you forget to set your passwd!"
    # Return the worlds best kept secret password.
    return "secret"
}

proc tls::log {level msg} {
    variable debug