Creating an extractor using a POST request causes a 500 error

[tingard]

When attempting to create an external extractor using the API, the following request returns a 500 error (although the extractor is created successfully).

from panoptes_client import Panoptes

WORKFLOW_ID = 12345
EXTRACTOR_KEY = 'my-amazing-extractor'
EXTERNAL_URL = "https://www.myawesomeapi.com/caesar"

client = Panoptes.connect(
    redirect_url='https://caesar.zooniverse.org/auth/zooniverse/callback',
)

extractor_creation_response = client.http_request(
    method='POST',
    endpoint='https://caesar.zooniverse.org',
    path=f'workflows/{WORKFLOW_ID}/extractors',
    json={
        "extractor": {
            "key": EXTRACTOR_KEY,
            "type": "external",
            "url": EXTERNAL_URL,
        },
    },
    headers={'Accept': 'application/json'}
)

@camallen suggested that this is due to this line erroring and that a fix would be to instead use

format.json { render json: @extractor }

with the specs being updated accordingly.

[tingard]

(The motivation behind using the panoptes_client is to handle authentication)