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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 validate_and_decode(jwt_bu64, cert_obj):
 """Example for validating the signature of a JWT using only the cryptography library. Note that this does NOT validate the claims in the claim set. """

    public_key = cert_obj.public_key()
    message = '.'.join(d1_common.cert.jwt.get_bu64_tup(jwt_bu64)[:2])
    signature = d1_common.cert.jwt.get_jwt_tup(jwt_bu64)[2]
    try:
        public_key.verify(
            signature,
            message,
            cryptography.hazmat.primitives.asymmetric.padding.PKCS1v15(),
            cryptography.hazmat.primitives.hashes.SHA256(),
        )
    except cryptography.exceptions.InvalidSignature as e:
        raise Exception('Signature is invalid. error="{}"'.format(str(e)))
    return d1_common.cert.jwt.get_jwt_dict(jwt_bu64)