See DRIVERS-320.

SNI support is only available in python's ssl module when SSLContext is available. Furthermore, SSLContext.wrap_socket will raise ValueError in some versions of python if the underlying OpenSSL version does not support SNI. The workaround is to check if ssl.HAS_SNI is True. The change to pool.py should look something like:

# global addition to pool.py
_HAVE_SNI = False
try:
    import ssl
    _HAVE_SNI = getattr(ssl, 'HAS_SNI', False)
except ImportError:
    pass

# change in pool._configured_socket
if _HAVE_SNI:
    sock = ssl_context.wrap_socket(sock, server_hostname=<hostname>)
else:
    sock = ssl_context.wrap_socket(sock)