RequestsCookieJar appends ".local" to cookie from localhost

When I make a request to localhost (on my development machine), Requests changes the domain from "localhost" to "localhost.local" when saving the cookie. Thus, I am unable to access the cookie if I specify the domain parameter in the get method.

My app requires me to get and set cookies on the session object as a persistence mechanism; I need to persist this cookie over more than one session in the python app.

Expected Result

I would expect the domain in RequestCookieJar to always match the domain I used to make the request.

Actual Result

If I make a request to localhost, instead I get the cookie saved to the domain "localhost.local". (Note that I cannot actually make requests to "localhost.local", they fail.) This puts me in a position where I must make requests to "localhost" but use "localhost.local" to get or set the cookie.

Reproduction Steps

>>> import requests
>>> ses = requests.Session()
>>> ses.get('http://localhost/')
<Response [200]>
>>> ses.cookies
<RequestsCookieJar[Cookie(version=0, name='PHPSESSID', value='ui1hr334bmcr1r85jlu8k3rq65', port=None, port_specified=False, domain='localhost.local', domain_specified=False, domain_initial_dot=False, path='/', path_specified=True, secure=False, expires=None, discard=True, comment=None, comment_url=None, rest={}, rfc2109=False)]>
>>> ses.cookies.get('PHPSESSID')
'ui1hr334bmcr1r85jlu8k3rq65'
>>> ses.cookies.get('PHPSESSID', domain='localhost')
>>> ses.cookies.get('PHPSESSID', domain='localhost.local')
'ui1hr334bmcr1r85jlu8k3rq65'

System Information

$ python -m requests.help

{
  "chardet": {
    "version": "3.0.4"
  },
  "cryptography": {
    "version": ""
  },
  "idna": {
    "version": "2.8"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.7.3"
  },
  "platform": {
    "release": "10",
    "system": "Windows"
  },
  "pyOpenSSL": {
    "openssl_version": "",
    "version": null
  },
  "requests": {
    "version": "2.22.0"
  },
  "system_ssl": {
    "version": "101000af"
  },
  "urllib3": {
    "version": "1.25.3"
  },
  "using_pyopenssl": false
}

Start by reproducing the localhost request and inspecting how the session's RequestsCookieJar stores cookie domains. Trace the cookie handling path responsible for changing localhost to localhost.local. Done means cookies from localhost retain the request domain and remain accessible through domain='localhost'.