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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 fetch_cluster_credentials(cls, db_user, db_name, cluster_id, duration_s):
 """Fetches temporary login credentials from AWS. The specified user must already exist in the database, or else an error will occur"""

        boto_client = boto3.client('redshift')

        try:
            return boto_client.get_cluster_credentials(
                DbUser=db_user,
                DbName=db_name,
                ClusterIdentifier=cluster_id,
                DurationSeconds=duration_s,
                AutoCreate=False)

        except boto_client.exceptions.ClientError as e:
            raise dbt.exceptions.FailedToConnectException(
                "Unable to get temporary Redshift cluster credentials: {}"
                .format(e))