'Returns the client\'s SSL certificate, if any.
To use client certificates, the HTTPServer\'s
`ssl.SSLContext.verify_mode` field must be set, e.g.::
ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
ssl_ctx.load_cert_chain("foo.crt", "foo.key")
ssl_ctx.load_verify_locations("cacerts.pem")
ssl_ctx.verify_mode = ssl.CERT_REQUIRED
server = HTTPServer(app, ssl_options=ssl_ctx)
By default, the return value is a dictionary (or None, if no
client certificate is present).  If ``binary_form`` is true, a
DER-encoded form of the certificate is returned instead.  See
SSLSocket.getpeercert() in the standard library for more
details.
http://docs.python.org/library/ssl.html#sslsocket-objects'

def get_ssl_certificate(self, binary_form=False):

    try:
        return self.connection.stream.socket.getpeercert(binary_form=binary_form)
    except SSLError:
        return None
