nl_tokens: Bucket 相关 查看是否存在该Bucket，是否有权限访问
pl_tokens: function headBucket ( params , callback ) { submitRequest . call ( this , { <mask> : 'name/cos:HeadBucket' , Bucket : params . Bucket , Region : params . Region , headers : params . Headers , method : 'HEAD' , } , function ( err , data ) { callback ( err , data ) ; } ) ; }