This function creates a temporary Mac keychain that we can use to work with
    credentials. This keychain uses a one-time password and a temporary file to
    store the data. We expect to have one keychain per socket. The returned
    SecKeychainRef must be freed by the caller, including calling
    SecKeychainDelete.

    Returns a tuple of the SecKeychainRef and the path to the temporary
    directory that contains it.

def _temporary_keychain():
    """
    This function creates a temporary Mac keychain that we can use to work with
    credentials. This keychain uses a one-time password and a temporary file to
    store the data. We expect to have one keychain per socket. The returned
    SecKeychainRef must be freed by the caller, including calling
    SecKeychainDelete.

    Returns a tuple of the SecKeychainRef and the path to the temporary
    directory that contains it.
    """
    # Unfortunately, SecKeychainCreate requires a path to a keychain. This
    # means we cannot use mkstemp to use a generic temporary file. Instead,
    # we're going to create a temporary directory and a filename to use there.
    # This filename will be 8 random bytes expanded into base64. We also need
    # some random bytes to password-protect the keychain we're creating, so we
    # ask for 40 random bytes.
    random_bytes = os.urandom(40)
    filename = base64.b16encode(random_bytes[:8]).decode('utf-8')
    password = base64.b16encode(random_bytes[8:])  # Must be valid UTF-8
    tempdirectory = tempfile.mkdtemp()

    keychain_path = os.path.join(tempdirectory, filename).encode('utf-8')

    # We now want to create the keychain itself.
    keychain = Security.SecKeychainRef()
    status = Security.SecKeychainCreate(
        keychain_path,
        len(password),
        password,
        False,
        None,
        ctypes.byref(keychain)
    )
    _assert_no_error(status)

    # Having created the keychain, we want to pass it off to the caller.
    return keychain, tempdirectory