KeyError: ‘HTTP_ACCESS_TOKEN’ : Flask with gevent WSGIServer

I am trying to take my Flask application to production with gevent WSGIServer

if __name__ == "__main__":

    app_host = "0.0.0.0"
    app_port = "8080"
    #app.run(host=app_host, port=app_port, debug=False)

    http_server = WSGIServer((app_host, app_port), app)
    logging.info("Starting the App server")
    http_server.serve_forever()

I am running the app server with gevent WSGIServer. Whenever I am trying to fetch any data like

token = request.headers["access_token"]

Receiving the following error

File "app.py", line 62, in post
token = request.headers["access_token"]
File "/home/shravan40/.local/lib/python3.6/site-packages/werkzeug/datastructures.py", line 1463, in __getitem__
return _unicodify_header_value(self.environ["HTTP_" + key])
KeyError: 'HTTP_ACCESS_TOKEN'
2020-08-03T18:01:31Z {'REMOTE_ADDR': '::ffff:127.0.0.1', 'REMOTE_PORT': '55088', 'HTTP_HOST': '127.0.0.1:8080', (hidden keys: 26)} failed with KeyError

Answer

pywsgi has something called SecureEnviron. This is intended to keep potentially sensitive information like HTTP authorization and cookies from being inadvertently printed or logged.

One can read more at the official documentation

Since I was passing access_token as key in the headers and trying to access the same from the code, it was raising KeyError: 'HTTP_ACCESS_TOKEN' because wasn’t part of whitelist_keys.

I used Authorization as header key and it worked like charm. The same can be done by adding access_token into the whitelist_keys.