Flowable REST API Query: support for an OR condition

The problem we are facing (and we have seen topics on the flowable forums about this in the past) is that we want to query a field with an OR condition from our front-end. We are calling the rest api query tasks.

For example: the front-end fetches tasks with taskInstanceVariable or processInstanceVariables "city", and we want the user to be able to select one or more cities.

We are looking for something like an IN operation type in addition to equals, like, lessThan, etc. With the value being an array of values:
{
"name" : "city",
"value" : ["Amsterdam", "Utrecht"],
"operation" : "in",
"type" : "string"
}