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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 request_signature(self, stringtosign):
 """ Construct a signature by making an RFC2104 HMAC-SHA1 of the following and converting it to Base64 UTF-8 encoded string. """

        digest = hmac.new(
            self.secret_key.encode(ENCODING),
            stringtosign.encode(ENCODING),
            hashlib.sha1
        ).digest()
        return b64_string(digest)