docs: function getTokens(rpcctx, options, callback) {
      var opts, log;
  
      assert.object(rpcctx, 'rpcctx');
      assert.object(options, 'options');
      assert.func(callback, 'callback');
  
      opts = { req_id: options.req_id || libuuid.create() };
      log = rpc.childLogger(rpcctx, opts);
      rpc.rpcCommonBufferData({
          'rpcctx': rpcctx,
          'rpcmethod': 'getTokens',
          'rpcargs': [ opts ],
          'log': log
      }, function (err, tokens) {
          if (!err && tokens.length != 1) {
              err = new VError('bad server response: expected 1 token, found %d',
                  tokens.length);
          }
  
          if (err) {
              callback(err);
              return;
          }
  
          callback(null, { 'tokens': tokens[0] });
      });
  }