[BUG][REGRESSION] external_auth over REST not working in 3007

[Foorack]

Description
The external REST auth stopped working after upgrade to 3007.

Worked in 3006.6. Broken in 3007.

Setup

• Hetzner Cloud VM
• Ubuntu 22.04 LTS with onedir
• Used Bootstrap to install

Steps to Reproduce the behavior
/etc/salt/master

external_auth:
  rest:
    ^url: http://localhost:8000/api/token

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
Running for trace purposes:

salt-master -l trace & salt-api -l trace

[INFO    ] [api_acl] Authentication not checked for user admin from IP 127.0.0.1
[DEBUG   ] Using selector: EpollSelector
[TRACE   ] ReqChannel send clear load={'eauth': 'rest', 'username': 'admin', 'password': 'password', 'cmd': 'mk_token'}
[TRACE   ] Clear payload received with command mk_token
[DEBUG   ] Reading configuration from /etc/salt/minion
[DEBUG   ] Including configuration from '/etc/salt/minion.d/_schedule.conf'
[DEBUG   ] Reading configuration from /etc/salt/minion.d/_schedule.conf
[DEBUG   ] Using cached minion ID from /etc/salt/minion_id: master
[DEBUG   ] Requesting URL http://localhost:8000/api/token using POST method
[DEBUG   ] Using backend: tornado
[TRACE   ] Request POST Data: {'password': 'password', 'username': 'admin'}
[DEBUG   ] Using selector: EpollSelector
[DEBUG   ] Authentication module threw Cannot run the event loop while another loop is running
[WARNING ] Authentication failure of type "eauth" occurred.
[WARNING ] Authentication failure of type "eauth" occurred.
[DEBUG   ] Closing AsyncReqChannel instance

Versions Report

salt --versions-report

Salt Version:
          Salt: 3007.0
 
Python Version:
        Python: 3.10.13 (main, Feb 19 2024, 03:31:20) [GCC 11.2.0]
 
Dependency Versions:
          cffi: 1.16.0
      cherrypy: unknown
      dateutil: 2.8.2
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 3.1.3
       libgit2: Not Installed
  looseversion: 1.3.0
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.7
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     packaging: 23.1
     pycparser: 2.21
      pycrypto: Not Installed
  pycryptodome: 3.19.1
        pygit2: Not Installed
  python-gnupg: 0.5.2
        PyYAML: 6.0.1
         PyZMQ: 25.1.2
        relenv: 0.15.1
         smmap: Not Installed
       timelib: 0.3.0
       Tornado: 6.3.3
           ZMQ: 4.3.4
 
Salt Package Information:
  Package Type: onedir
 
System Versions:
          dist: ubuntu 22.04.4 jammy
        locale: utf-8
       machine: x86_64
       release: 6.5.0-27-generic
        system: Linux
       version: Ubuntu 22.04.4 jammy

[Foorack]

Possibly related to #66194 due to shared error message:

Cannot run the event loop while another loop is running