socket, but must provide bi-directional flow. Also
	setting session parameters for SSL handshake.</dd>

<blockquote>
    <dl>
	<dt><strong>-alpn</strong> <em>list</em></dt>
	<dd>List of protocols to offer during Application-Layer
	    Protocol Negotiation (ALPN). For example: <em>h2</em> and
	    <em>http/1.1</em>, but not <em>h3</em> or <em>quic</em>.</dd>
	<dt><strong>-cadir</strong> <em>dir</em></dt>
	<dd>Set the CA certificates path. The default directory is platform
	    specific and can be set at compile time. This can be overridden
	    via the <b>SSL_CERT_DIR</b> environment variable.</dd>
	<dt><strong>-cafile </strong><em>filename</em></dt>
	<dd>Set the certificate authority (CA) certificates file. The default
	    is the cert.pem file in the OpsnSSL directory. This can also be

<p>
As indicated above, individual channels can be given their own callbacks
to handle intermediate processing by the OpenSSL library, using the
<strong>-command</strong>, <strong>-password</strong>, and
<strong>-validate_command</strong> options passed to either of
<strong>tls::socket</strong> or <strong>tls::import</strong>.
If the callback generates an error, the <b>bgerror</b> command with be
invoked with the error information.
</p>

<blockquote>
<dl>

    <dt><strong>-command</strong> <em>callback</em></dt>
    <dd>
	Invokes the specified <em>callback</em> script at several points
	during the OpenSSL handshake and use. See below for the possible
	arguments passed to the callback script. Values returned from the
	callback are ignored.


	<br>
	<br>

	<dl>

	<dt>

	  <ul>
	  <li>Possible values for <em>major</em> are:
	  <code>handshake, alert, connect, accept</code>.</li>
	  <li>Possible values for <em>minor</em> are:
	  <code>start, done, read, write, loop, exit</code>.</li>
	  <li>The <em>message</em> argument is a descriptive string which may
	  be generated either by <code>SSL_state_string_long()</code> or by
	  <code>SSL_alert_desc_string_long()</code>, depending on the context.</li>
	  <li>For alerts, the possible values for <em>type</em> are:
	  <code>warning, fatal, and unknown</code>. For others,
	  <code>info</code> is used.</li>
	  </ul>
	</dd>

	<dt>

    </dd>

    <br>

    <dt><strong>-password</strong> <em>callback</em></dt>
    <dd>
	Invokes the specified <em>callback</em> script when OpenSSL needs to
	obtain a password. See below for the possible arguments passed to
	the callback script. See below for valid return values.

	<br>
	<br>

	<dl>

	<dt>
	  <strong>password</strong> <em>rwflag size</em>
	</dt>
	<dd>
	  Invoked when loading or storing a PEM certificate with encryption.
	  Where <em>rwflag</em> is 0 for reading/decryption or 1 for
	  writing/encryption (can prompt user to confirm) and
	  <em>size</em> is the max password length in bytes.
	  The callback should return the password as a string.

	</dd>
    </dd>

    <br>


    <dt><strong>-validatecommand</strong> <em>callback</em></dt>
    <dd>
	Invokes the specified <em>callback</em> script during handshake in
	order to validate the provided value(s). See below for the possible
	arguments passed to the callback script.
	To reject the value and abort connection, the callback should return 0.
	To accept the value and continue the connection, it should return 1.
	To reject the value, but continue the connection, it should return 2.

	<br>
	<br>

	<dl>

	<dt>
	  <strong>alpn</strong> <em>protocol</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked when the client ALPN
	  extension is received. Where <em>protocol</em> is the first
	  <b>-alpn</b> specified protocol common to the both the client and
	  server. If none, the first client specified protocol is used.
	  Called after hello and ALPN callbacks.
	</dd>

	<br>

	<dt>
	  <strong>hello</strong> <em>servername</em>
	</dt>

}

/*
 *-------------------------------------------------------------------
 *
 * Password Callback --
 *
 *	Called when a password for a private key loading/storing a PEM
 *	certificate with encryption. Evals callback script and returns
 *	the result as the password string in buf.
 *
 * Results:
 *	None
 *
 * Side effects:
 *	Calls callback (if defined)
 *
 * Returns:
 *	Password size in bytes or -1 for an error.
 *
 *-------------------------------------------------------------------
 */
static int
PasswordCallback(char *buf, int size, int rwflag, void *udata) {
    State *statePtr	= (State *) udata;
    Tcl_Interp *interp	= statePtr->interp;
    Tcl_Obj *cmdPtr;
    int code;

    dprintf("Called");

    /* If no callback, use default callback */
    if (statePtr->password == NULL) {
	if (Tcl_EvalEx(interp, "tls::password", -1, TCL_EVAL_GLOBAL) == TCL_OK) {
	    char *ret = (char *) Tcl_GetStringResult(interp);
	    strncpy(buf, ret, (size_t) size);
	    return (int)strlen(ret);
	} else {
	    return -1;
	}
    }

    /* Create command to eval */
    cmdPtr = Tcl_DuplicateObj(statePtr->password);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("password", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewIntObj(rwflag));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewIntObj(size));

    Tcl_Preserve((ClientData) interp);
    Tcl_Preserve((ClientData) statePtr);

    /* Eval callback command */
    Tcl_IncrRefCount(cmdPtr);
    code = Tcl_EvalObjEx(interp, cmdPtr, TCL_EVAL_GLOBAL);
    if (code != TCL_OK) {
#if (TCL_MAJOR_VERSION == 8) && (TCL_MINOR_VERSION < 6)
	Tcl_BackgroundError(interp);
#else
	Tcl_BackgroundException(interp, code);
#endif
    }
    Tcl_DecrRefCount(cmdPtr);

    Tcl_Release((ClientData) statePtr);

    /* If successful, pass back password string and truncate if too long */
    if (code == TCL_OK) {
	int len;
	char *ret = (char *) Tcl_GetStringFromObj(Tcl_GetObjResult(interp), &len);
	if (len > size-1) {
	    len = size-1;
	}
	strncpy(buf, ret, (size_t) len);
	buf[len] = '\0';
	Tcl_Release((ClientData) interp);
	return(len);

    }
    Tcl_Release((ClientData) interp);
    return -1;

}

/*
 *-------------------------------------------------------------------
 *
 * Session Callback for Clients --
 *