When JWT is incorrect, the returned error should be 400 Bad Request and not 500

[uaru]

Description

When the server receives the request authorized with JWT with payload

{
   :sub => username,
   :'_couchdb.roles' => roles,
   :exp => ...,
}

and roles is a string, the server returns error 500 Internal Server Error with

{
  "error": "internal_server_error",
  "reason": "No DB shards could be opened.",
  "ref": ...
}

Steps to Reproduce

curl -X GET --location "https://<couchdb_server>:6984/<db>/<document>" \
    -H "Accept: application/json" \
    -H "Content-Type: application/json; charset=utf-8" \
    -H "Authorization: Bearer <JWT Token>"

The server return error 500, with body:

{
  "error": "internal_server_error",
  "reason": "No DB shards could be opened.",
  "ref": ...
}

Expected Behaviour

The server should return 400 Bad Request.

Your Environment

Server: CouchDB/3.2.1 (Erlang OTP/23)

Running in Docker on Ubuntu 18.04

[big-r81]

Fixed by #3960.