DRF User Serializer.

GET /api/users/
HTTP 200 OK
Allow: GET, POST, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

[
    {
        "id": 1,
        "username": "john"
    },
    {
        "id": 2,
        "username": "mac"
    },
    {
        "id": 3,
        "username": "pkraus"
    }
]
Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only.