GET /api/connections/username/{username} fails with a 500

[SimonUnge]

Describe the bug

Calling GET /api/connections/username as a policymaker/management user leads to 500 internal error.

Calling DETETE on /api/connections/username as policymaker/monitor/management user leads to 500 internal error.

Reproduction steps

1. Create a user with policymaker tag
2. run GET on /api/connections/username/SOMEOTHERUSER
   ...

Expected behavior

401 Unauthorized

Additional context

No response

[michaelklishin]

Here is the stack trace:

exception error: bad argument
  in function  lists:keyfind/3
  called as lists:keyfind(user,1,not_found)
   *** argument 3: not a list
  in call from rabbit_misc:pget/2 (rabbit_misc.erl, line 899)
  in call from rabbit_mgmt_util:'-is_authorized_user/3-fun-0-'/3 (rabbit_mgmt_util.erl, line 188)
  in call from rabbit_mgmt_util:is_authorized/7 (rabbit_mgmt_util.erl, line 285)
  in call from rabbit_mgmt_wm_connection:is_authorized/2 (rabbit_mgmt_wm_connection.erl, line 63)
  in call from cowboy_rest:call/3 (cowboy_rest.erl, line 1583)
  in call from cowboy_rest:is_authorized/2 (cowboy_rest.erl, line 368)
  in call from cowboy_rest:upgrade/4 (cowboy_rest.erl, line 284)