RESTful API: get/set one "global" single resource without id - api

Question

TL;DR
In my current API, I've got two endpoints to handle the context:
GET /context/get
POST /context/set '{"id": "123"}'
What's the recommended way of having this global, id-less state accessible from RESTful API?
Please assume that the context concept can't be changed.
Background
Let's say I've got a user that is logged. He's by default assigned to a context that he can change.
After the context change, all the subsequent API calls will return different data, according to the context.
Example:
// Backend
Context = "Poland"
then
$ curl -X GET http://api.myapp.com/cities
will respond:
{
"cities": [{
"id": "1",
"name": Warszawa"
}, {
"id": "2",
"name": Wrocław"
}]
}
However, if you change the context:
// Backend
Context = "USA"
then, the same URL:
$ curl -X GET http://api.myapp.com/cities
should return the different set of data:
{
"cities": [{
"id": "3",
"name": New York City"
}, {
"id": "4",
"name": Boston"
}]
}
Question
As the context is just a global state on the backend side, it doesn't have an id. It doesn't belong to any collection either. Still, I want it to be accessible in the API. There are three possible solutions I see:
Solution #1 - existing
Set a context
$ curl -X POST http://api.myapp.com/context/set '{"id": "123"}'
Get a context
$ curl -X GET http://api.myapp.com/context/get
This one doesn't really feel like a RESTful API and still, on the frontend side, I have to mock the id (using ember-data). And the resource name is singular instead of plural.
Solution #2 - mocking the id
Set a context
$ curl -X POST http://api.myapp.com/context/1 '{"contextId": "123"}'
Get a context
$ curl -X GET http://api.myapp.com/context/1
Here I mock the id to always equal to one but I feel that it's super hacky and certainly not self-explanatory... Moreover, I've got a name conflict: id vs contextId. And the resource name is singular instead of plural.
Solution #3 - actions
Set a context
$ curl -X POST http://api.myapp.com/context/actions/set '{"id": "123"}'
Get a context
$ curl -X GET http://api.myapp.com/context/actions/get
This is very similar to the first one but using actions that could be a part of my whole API design (taken from e.g. gocardless. Still, I'll have a problem how to model it on the frontend side nicely. And the resource name is singular instead of plural again.
Is there any #4 option? How should I address this problem?
Thanks!

Answer 1

Your three solutions are RPC, not REST. Not only they are not stateless, but setting a resource to some other resource by setting an id is very RCP'ish.
A RESTful solution, if you really want to go that way, is to set the context in a header. The client should send a header like X-ContextId or something like that, and you determine the request context you need from that.
However, don't worry too much about being RESTful if that's not what your application requires. I recommend reading the answer here: SOAP vs REST (differences)

Answer 2

What's the recommended way of having this global, id-less state
accessible from RESTful API?
A RESTful API is by definition stateless, no client context should be stored on the server between requests.
If you want your API to be RESTful, you'll have to pass this id with each request.