def make_ssl_devcert(
    base_path: str, host: str | None = None, cn: str | None = None
) -> tuple[str, str]:
    """Creates an SSL key for development.  This should be used instead of
    the ``'adhoc'`` key which generates a new cert on each server start.
    It accepts a path for where it should store the key and cert and
    either a host or CN.  If a host is given it will use the CN
    ``*.host/CN=host``.

    For more information see :func:`run_simple`.

    .. versionadded:: 0.9

    :param base_path: the path to the certificate and key.  The extension
                      ``.crt`` is added for the certificate, ``.key`` is
                      added for the key.
    :param host: the name of the host.  This can be used as an alternative
                 for the `cn`.
    :param cn: the `CN` to use.
    """

    if host is not None:
        cn = host
    cert, pkey = generate_adhoc_ssl_pair(cn=cn)

    from cryptography.hazmat.primitives import serialization

    cert_file = f"{base_path}.crt"
    pkey_file = f"{base_path}.key"

    with open(cert_file, "wb") as f:
        f.write(cert.public_bytes(serialization.Encoding.PEM))
    with open(pkey_file, "wb") as f:
        f.write(
            pkey.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.TraditionalOpenSSL,
                encryption_algorithm=serialization.NoEncryption(),
            )
        )

    return cert_file, pkey_file
Creates an SSL key for development.  This should be used instead of
    the ``'adhoc'`` key which generates a new cert on each server start.
    It accepts a path for where it should store the key and cert and
    either a host or CN.  If a host is given it will use the CN
    ``*.host/CN=host``.

    For more information see :func:`run_simple`.

    .. versionadded:: 0.9

    :param base_path: the path to the certificate and key.  The extension
                      ``.crt`` is added for the certificate, ``.key`` is
                      added for the key.
    :param host: the name of the host.  This can be used as an alternative
                 for the `cn`.
    :param cn: the `CN` to use.
    
src/werkzeug/serving.py