salt: Salt-master doesn't renew vault token

Description of Issue/Question

Vault allows for an issued token to be renewed while it is still active. When the salt-master is configured to use token auth, it does not attempt to renew the token, instead, it lets it expire and then fail.

This seems like poor behavior, especially since the other auth method approle appears to validate if it’s expired and request a new token. (older versions of salt do not support approle).

It would be beneficial if the salt-master monitored the remaining time to live of it’s configured token and renew’d it.

Setup

(Please provide relevant configs and/or SLS files (Be sure to remove sensitive info).)

/etc/salt/master.d/vault.conf
vault:
  url: http://avault.server:8200
  auth:
    method: token
    token: randomjunkhere

Steps to Reproduce Issue

Provision a token with the appropriate polices, wait until the ttl expires, be unable to access vault.

Versions Report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

salt --versions-report
Salt Version:
           Salt: 2017.7.8

Dependency Versions:
           cffi: 1.5.2
       cherrypy: Not Installed
       dateutil: 2.4.2
      docker-py: Not Installed
          gitdb: 2.0.3
      gitpython: 2.1.10
          ioflo: Not Installed
         Jinja2: 2.8
        libgit2: 0.24.0
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: 1.0.3
   msgpack-pure: Not Installed
 msgpack-python: 0.4.6
   mysql-python: Not Installed
      pycparser: 2.14
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: 0.24.0
         Python: 2.7.12 (default, Nov 12 2018, 14:36:49)
   python-gnupg: 0.3.8
         PyYAML: 3.11
          PyZMQ: 15.2.0
           RAET: Not Installed
          smmap: 2.0.3
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.1.4

System Versions:
           dist: Ubuntu 16.04 xenial
         locale: UTF-8
        machine: x86_64
        release: 4.4.0-1075-aws
         system: Linux
        version: Ubuntu 16.04 xenial