How do I get the user ID through the API

How do I get the userid through the API to then insert it into requests

-X PUT ‘https://URL/index.php/apps/deck/api/v1.0/boards/62/stacks/186/cards/259/assignUser’ -d “userid= ?”
-X PUT ‘https://URL/index.php/apps/deck/api/v1.0/boards/62/stacks/186/cards/259/unassignUser’ -d “userid= ?”

When requesting card information

{
“title”: “test2”,
“description”: null,
“stackId”: 185,
“type”: “plaint”,
“lastModified”: 1549030970,
“lastEditor”: null,
“createdAt”: 1549030970,
“labels”: [],
“assignedUsers”: [{
“id”: 70,
“participant”: {
“primaryKey”: “a.potapov”,
“uid”: “a.potapov”,
“displayname”: “\u0410\u043d\u0434\u0440\u0435\u0439 \u041f\u043e\u0442\u0430\u043f\u043e\u0432”
},
“cardId”: 259
}],
“attachments”: [],
“attachmentCount”: 0,
“owner”: {
“primaryKey”: “n.gamzin”,
“uid”: “n.gamzin”,
“displayname”: “\u041d\u0438\u043a\u043e\u043b\u0430\u0439 \u0413\u0430\u043c\u0437\u0438\u043d”
},
“order”: 1,
“archived”: false,
“duedate”: null,
“deletedAt”: 0,
“commentsUnread”: 0,
“id”: 259,
“overdue”: 0