def from_http(cls, headers: Mapping[str, str], body: bytes,
                  *, secret: Optional[str] = None) -> "Event":
        """Construct an event from HTTP headers and JSON body data.

        The mapping providing the headers is expected to support lowercase keys.

        Since this method assumes the body of the HTTP request is JSON, a check
        is performed for a content-type of "application/json" (GitHub does
        support other content-types). If the content-type does not match,
        BadRequest is raised.

        If the appropriate headers are provided for event validation, then it
        will be performed unconditionally. Any failure in validation
        (including not providing a secret) will lead to ValidationFailure being
        raised.
        """
        if "x-hub-signature" in headers:
                if secret is None:
                    raise ValidationFailure("secret not provided")
                validate_event(body, signature=headers["x-hub-signature"],
                               secret=secret)
        elif secret is not None:
            raise ValidationFailure("signature is missing")

        try:
            data = _decode_body(headers["content-type"], body, strict=True)
        except (KeyError, ValueError) as exc:
            raise BadRequest(http.HTTPStatus(415),
                             "expected a content-type of "
                             "'application/json' or "
                             "'application/x-www-form-urlencoded'") from exc
        return cls(data, event=headers["x-github-event"],
                   delivery_id=headers["x-github-delivery"])
Construct an event from HTTP headers and JSON body data.

        The mapping providing the headers is expected to support lowercase keys.

        Since this method assumes the body of the HTTP request is JSON, a check
        is performed for a content-type of "application/json" (GitHub does
        support other content-types). If the content-type does not match,
        BadRequest is raised.

        If the appropriate headers are provided for event validation, then it
        will be performed unconditionally. Any failure in validation
        (including not providing a secret) will lead to ValidationFailure being
        raised.