--- a/mercurial/help/config.txt	Thu Mar 09 22:35:10 2017 -0800
+++ b/mercurial/help/config.txt	Thu Mar 09 22:40:52 2017 -0800
@@ -323,12 +323,32 @@
 ``auth``
 --------
 
-Authentication credentials for HTTP authentication. This section
-allows you to store usernames and passwords for use when logging
-*into* HTTP servers. See :hg:`help config.web` if
-you want to configure *who* can login to your HTTP server.
-
-Each line has the following format::
+Authentication credentials and other authentication-like configuration
+for HTTP connections. This section allows you to store usernames and
+passwords for use when logging *into* HTTP servers. See
+:hg:`help config.web` if you want to configure *who* can login to
+your HTTP server.
+
+The following options apply to all hosts.
+
+``cookiefile``
+    Path to a file containing HTTP cookie lines. Cookies matching a
+    host will be sent automatically.
+
+    The file format uses the Mozilla cookies.txt format, which defines cookies
+    on their own lines. Each line contains 7 fields delimited by the tab
+    character (domain, is_domain_cookie, path, is_secure, expires, name,
+    value). For more info, do an Internet search for "Netscape cookies.txt
+    format."
+
+    Note: the cookies parser does not handle port numbers on domains. You
+    will need to remove ports from the domain for the cookie to be recognized.
+    This could result in a cookie being disclosed to an unwanted server.
+
+    The cookies file is read-only.
+
+Other options in this section are grouped by name and have the following
+format::
 
     <name>.<argument> = <value>
 

--- a/mercurial/url.py	Thu Mar 09 22:35:10 2017 -0800
+++ b/mercurial/url.py	Thu Mar 09 22:40:52 2017 -0800
@@ -417,6 +417,35 @@
         else:
             return None
 
+class cookiehandler(urlreq.basehandler):
+    def __init__(self, ui):
+        self.cookiejar = None
+
+        cookiefile = ui.config('auth', 'cookiefile')
+        if not cookiefile:
+            return
+
+        cookiefile = util.expandpath(cookiefile)
+        try:
+            cookiejar = util.cookielib.MozillaCookieJar(cookiefile)
+            cookiejar.load()
+            self.cookiejar = cookiejar
+        except util.cookielib.LoadError as e:
+            ui.warn(_('(error loading cookie file %s: %s; continuing without '
+                      'cookies)\n') % (cookiefile, str(e)))
+
+    def http_request(self, request):
+        if self.cookiejar:
+            self.cookiejar.add_cookie_header(request)
+
+        return request
+
+    def https_request(self, request):
+        if self.cookiejar:
+            self.cookiejar.add_cookie_header(request)
+
+        return request
+
 handlerfuncs = []
 
 def opener(ui, authinfo=None):
@@ -450,6 +479,7 @@
     handlers.extend((httpbasicauthhandler(passmgr),
                      httpdigestauthhandler(passmgr)))
     handlers.extend([h(ui, passmgr) for h in handlerfuncs])
+    handlers.append(cookiehandler(ui))
     opener = urlreq.buildopener(*handlers)
 
     # The user agent should should *NOT* be used by servers for e.g.

--- a/tests/test-http.t	Thu Mar 09 22:35:10 2017 -0800
+++ b/tests/test-http.t	Thu Mar 09 22:40:52 2017 -0800
@@ -1,4 +1,4 @@
-#require serve
+#require killdaemons serve
 
   $ hg init test
   $ cd test
@@ -333,3 +333,64 @@
   abort: pull failed on remote
   [255]
   $ cat error.log
+
+corrupt cookies file should yield a warning
+
+  $ cat > $TESTTMP/cookies.txt << EOF
+  > bad format
+  > EOF
+
+  $ hg --config auth.cookiefile=$TESTTMP/cookies.txt id http://localhost:$HGPORT/
+  (error loading cookie file $TESTTMP/cookies.txt: '$TESTTMP/cookies.txt' does not look like a Netscape format cookies file; continuing without cookies)
+  56f9bc90cce6
+
+  $ killdaemons.py
+
+Create dummy authentication handler that looks for cookies. It doesn't do anything
+useful. It just raises an HTTP 500 with details about the Cookie request header.
+We raise HTTP 500 because its message is printed in the abort message.
+
+  $ cat > cookieauth.py << EOF
+  > from mercurial import util
+  > from mercurial.hgweb import common
+  > def perform_authentication(hgweb, req, op):
+  >     cookie = req.env.get('HTTP_COOKIE')
+  >     if not cookie:
+  >         raise common.ErrorResponse(common.HTTP_SERVER_ERROR, 'no-cookie')
+  >     raise common.ErrorResponse(common.HTTP_SERVER_ERROR, 'Cookie: %s' % cookie)
+  > def extsetup():
+  >     common.permhooks.insert(0, perform_authentication)
+  > EOF
+
+  $ hg serve --config extensions.cookieauth=cookieauth.py -R test -p $HGPORT -d --pid-file=pid
+  $ cat pid > $DAEMON_PIDS
+
+Request without cookie sent should fail due to lack of cookie
+
+  $ hg id http://localhost:$HGPORT
+  abort: HTTP Error 500: no-cookie
+  [255]
+
+Populate a cookies file
+
+  $ cat > cookies.txt << EOF
+  > # HTTP Cookie File
+  > # Expiration is 2030-01-01 at midnight
+  > .example.com	TRUE	/	FALSE	1893456000	hgkey	examplevalue
+  > EOF
+
+Should not send a cookie for another domain
+
+  $ hg --config auth.cookiefile=cookies.txt id http://localhost:$HGPORT/
+  abort: HTTP Error 500: no-cookie
+  [255]
+
+Add a cookie entry for our test server and verify it is sent
+
+  $ cat >> cookies.txt << EOF
+  > localhost.local	FALSE	/	FALSE	1893456000	hgkey	localhostvalue
+  > EOF
+
+  $ hg --config auth.cookiefile=cookies.txt id http://localhost:$HGPORT/
+  abort: HTTP Error 500: Cookie: hgkey=localhostvalue
+  [255]