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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 _build_signature(self):
 """Create the signature using the private key."""

        sig_contents = \
            self.payload + "." + \
            b64encode(b"application/xml").decode("ascii") + "." + \
            b64encode(b"base64url").decode("ascii") + "." + \
            b64encode(b"RSA-SHA256").decode("ascii")
        sig_hash = SHA256.new(sig_contents.encode("ascii"))
        cipher = PKCS1_v1_5.new(self.private_key)
        sig = urlsafe_b64encode(cipher.sign(sig_hash))
        key_id = urlsafe_b64encode(bytes(self.author_handle, encoding="utf-8"))
        return sig, key_id