Is it possible to assign an issue to a user with the REST API using the user's key?

[Niels Frederiksen]

Hi,
I am trying to assign an issue to a user with the REST api, but I only have the user's unique "key" available.
I know I can get the "name" from the "key" via the api, but it's for a big batch job so I am trying to avoid the extra api call.
I have been trying to use the "/rest/api/2/issue/{issueIdOrKey}/assignee" endpoint, but it only works when I send the "name".
If I send the "key" I still get "204 No Content", but the issue is not assigned to the user.
Since "key" is one of the properties in the schema, I am guessing that this may be a bug but I am not sure.
If I use the normal Edit Issue endpoint I get "Bad Request" if I send anything other than a "name"

Anyone know if this is possible, or am I forced to fetch the name from the API?