te</code> is an optional handler for unverifiable certificates.
The handler receives the <a href="dart-io/X509Certificate-class.html">X509Certificate</a>, and can inspect it and
decide (or let the user decide) whether to accept
the connection or not.  The handler should return true
to continue the <a href="dart-io/SecureSocket-class.html">SecureSocket</a> connection.</p>
<p><code>supportedProtocols</code> is an optional list of protocols (in decreasing
order of preference) to use during the ALPN protocol ne