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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 cli(env, identifier):
 """List virtual server credentials."""


    vsi = SoftLayer.VSManager(env.client)
    vs_id = helpers.resolve_id(vsi.resolve_ids, identifier, 'VS')
    instance = vsi.get_instance(vs_id)

    table = formatting.Table(['username', 'password'])
    for item in instance['operatingSystem']['passwords']:
        table.add_row([item['username'], item['password']])
    env.fout(table)