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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def deserialize_header_auth(stream, algorithm, verifier=None):
 """Deserializes a MessageHeaderAuthentication object from a source stream. :param stream: Source data stream :type stream: io.BytesIO :param algorithm: The AlgorithmSuite object type contained in the header :type algorith: aws_encryption_sdk.identifiers.AlgorithmSuite :param verifier: Signature verifier object (optional) :type verifier: aws_encryption_sdk.internal.crypto.Verifier :returns: Deserialized MessageHeaderAuthentication object :rtype: aws_encryption_sdk.internal.structures.MessageHeaderAuthentication """

    _LOGGER.debug("Starting header auth deserialization")
    format_string = ">{iv_len}s{tag_len}s".format(iv_len=algorithm.iv_len, tag_len=algorithm.tag_len)
    return MessageHeaderAuthentication(*unpack_values(format_string, stream, verifier))