def prepare_str_to_sign(req_tgt, hdrs):
    """
    Concatenates Intersight headers in preparation to be RSA signed

    :param req_tgt : http method plus endpoint
    :param hdrs: dict with header keys
    :return: concatenated header authorization string
    """
    ss = ''
    ss = ss + '(request-target): ' + req_tgt.lower() + '\n'
    length = len(hdrs.items())
    i = 0
    for key, value in hdrs.items():
        ss = ss + key.lower() + ': ' + value
        if i < length - 1:
            ss = ss + '\n'
        i += 1
    return ss
