prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Passwords beginning or ending with a whitespace are not supported
  Due to POST argument stripping, passwords with a beginning or ending whitespace are not allowed.
  
  **How to reproduce the issue**
  Set up a user password with an ending or beginning whitespace.
  
  **What you expected to happen**
  The user should be allowed to login with the password, given that the password should be any complicated sequence of characters the user can reproduce.
  
  **What actually happens**
  The user is denied access, because the LoginHandler will strip all posted values before considering the password for authentication (line 81, get_argument has a default "strip=True")
  
  **Share what version of JupyterHub you are using**
  HEAD (006488fc749923851df97d47d8850bdf5fd157cf)
  
  
  
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `jupyterhub/handlers/login.py`
  Content:
  ```
  1 """HTTP Handlers for the hub server"""
  2 
  3 # Copyright (c) Jupyter Development Team.
  4 # Distributed under the terms of the Modified BSD License.
  5 
  6 from urllib.parse import urlparse
  7 
  8 from tornado.escape import url_escape
  9 from tornado import gen
  10 from tornado.httputil import url_concat
  11 
  12 from .base import BaseHandler
  13 
  14 
  15 class LogoutHandler(BaseHandler):
  16     """Log a user out by clearing their login cookie."""
  17     def get(self):
  18         user = self.get_current_user()
  19         if user:
  20             self.log.info("User logged out: %s", user.name)
  21             self.clear_login_cookie()
  22             self.statsd.incr('logout')
  23         if self.authenticator.auto_login:
  24             self.render('logout.html')
  25         else:
  26             self.redirect(self.settings['login_url'], permanent=False)
  27 
  28 
  29 class LoginHandler(BaseHandler):
  30     """Render the login page."""
  31 
  32     def _render(self, login_error=None, username=None):
  33         return self.render_template('login.html',
  34                 next=url_escape(self.get_argument('next', default='')),
  35                 username=username,
  36                 login_error=login_error,
  37                 custom_html=self.authenticator.custom_html,
  38                 login_url=self.settings['login_url'],
  39                 authenticator_login_url=self.authenticator.login_url(self.hub.server.base_url),
  40         )
  41 
  42     def get(self):
  43         self.statsd.incr('login.request')
  44         next_url = self.get_argument('next', '')
  45         if (next_url + '/').startswith('%s://%s/' % (self.request.protocol, self.request.host)):
  46             # treat absolute URLs for our host as absolute paths:
  47             next_url = urlparse(next_url).path
  48         elif not next_url.startswith('/'):
  49             # disallow non-absolute next URLs (e.g. full URLs to other hosts)
  50             next_url = ''
  51         user = self.get_current_user()
  52         if user:
  53             if not next_url:
  54                 if user.running:
  55                     next_url = user.url
  56                 else:
  57                     next_url = self.hub.server.base_url
  58             # set new login cookie
  59             # because single-user cookie may have been cleared or incorrect
  60             self.set_login_cookie(self.get_current_user())
  61             self.redirect(next_url, permanent=False)
  62         else:
  63             if self.authenticator.auto_login:
  64                 auto_login_url = self.authenticator.login_url(self.hub.server.base_url)
  65                 if auto_login_url == self.settings['login_url']:
  66                     self.authenticator.auto_login = False
  67                     self.log.warning("Authenticator.auto_login cannot be used without a custom login_url")
  68                 else:
  69                     if next_url:
  70                         auto_login_url = url_concat(auto_login_url, {'next': next_url})
  71                     self.redirect(auto_login_url)
  72                     return
  73             username = self.get_argument('username', default='')
  74             self.finish(self._render(username=username))
  75 
  76     @gen.coroutine
  77     def post(self):
  78         # parse the arguments dict
  79         data = {}
  80         for arg in self.request.arguments:
  81             data[arg] = self.get_argument(arg)
  82 
  83         auth_timer = self.statsd.timer('login.authenticate').start()
  84         username = yield self.authenticate(data)
  85         auth_timer.stop(send=False)
  86 
  87         if username:
  88             self.statsd.incr('login.success')
  89             self.statsd.timing('login.authenticate.success', auth_timer.ms)
  90             user = self.user_from_username(username)
  91             already_running = False
  92             if user.spawner:
  93                 status = yield user.spawner.poll()
  94                 already_running = (status == None)
  95             if not already_running and not user.spawner.options_form:
  96                 yield self.spawn_single_user(user)
  97             self.set_login_cookie(user)
  98             next_url = self.get_argument('next', default='')
  99             if not next_url.startswith('/'):
  100                 next_url = ''
  101             next_url = next_url or self.hub.server.base_url
  102             self.redirect(next_url)
  103             self.log.info("User logged in: %s", username)
  104         else:
  105             self.statsd.incr('login.failure')
  106             self.statsd.timing('login.authenticate.failure', auth_timer.ms)
  107             self.log.debug("Failed login for %s", data.get('username', 'unknown user'))
  108             html = self._render(
  109                 login_error='Invalid username or password',
  110                 username=username,
  111             )
  112             self.finish(html)
  113 
  114 
  115 # /login renders the login page or the "Login with..." link,
  116 # so it should always be registered.
  117 # /logout clears cookies.
  118 default_handlers = [
  119     (r"/login", LoginHandler),
  120     (r"/logout", LogoutHandler),
  121 ]
  122
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/jupyterhub/handlers/login.py b/jupyterhub/handlers/login.py
  --- a/jupyterhub/handlers/login.py
  +++ b/jupyterhub/handlers/login.py
  @@ -78,7 +78,7 @@
           # parse the arguments dict
           data = {}
           for arg in self.request.arguments:
  -            data[arg] = self.get_argument(arg)
  +            data[arg] = self.get_argument(arg, strip=False)
   
           auth_timer = self.statsd.timer('login.authenticate').start()
           username = yield self.authenticate(data)
  
verification_info: {"golden_diff": "diff --git a/jupyterhub/handlers/login.py b/jupyterhub/handlers/login.py\n--- a/jupyterhub/handlers/login.py\n+++ b/jupyterhub/handlers/login.py\n@@ -78,7 +78,7 @@\n         # parse the arguments dict\n         data = {}\n         for arg in self.request.arguments:\n-            data[arg] = self.get_argument(arg)\n+            data[arg] = self.get_argument(arg, strip=False)\n \n         auth_timer = self.statsd.timer('login.authenticate').start()\n         username = yield self.authenticate(data)\n", "issue": "Passwords beginning or ending with a whitespace are not supported\nDue to POST argument stripping, passwords with a beginning or ending whitespace are not allowed.\r\n\r\n**How to reproduce the issue**\r\nSet up a user password with an ending or beginning whitespace.\r\n\r\n**What you expected to happen**\r\nThe user should be allowed to login with the password, given that the password should be any complicated sequence of characters the user can reproduce.\r\n\r\n**What actually happens**\r\nThe user is denied access, because the LoginHandler will strip all posted values before considering the password for authentication (line 81, get_argument has a default \"strip=True\")\r\n\r\n**Share what version of JupyterHub you are using**\r\nHEAD (006488fc749923851df97d47d8850bdf5fd157cf)\r\n\r\n\r\n\n", "before_files": [{"content": "\"\"\"HTTP Handlers for the hub server\"\"\"\n\n# Copyright (c) Jupyter Development Team.\n# Distributed under the terms of the Modified BSD License.\n\nfrom urllib.parse import urlparse\n\nfrom tornado.escape import url_escape\nfrom tornado import gen\nfrom tornado.httputil import url_concat\n\nfrom .base import BaseHandler\n\n\nclass LogoutHandler(BaseHandler):\n    \"\"\"Log a user out by clearing their login cookie.\"\"\"\n    def get(self):\n        user = self.get_current_user()\n        if user:\n            self.log.info(\"User logged out: %s\", user.name)\n            self.clear_login_cookie()\n            self.statsd.incr('logout')\n        if self.authenticator.auto_login:\n            self.render('logout.html')\n        else:\n            self.redirect(self.settings['login_url'], permanent=False)\n\n\nclass LoginHandler(BaseHandler):\n    \"\"\"Render the login page.\"\"\"\n\n    def _render(self, login_error=None, username=None):\n        return self.render_template('login.html',\n                next=url_escape(self.get_argument('next', default='')),\n                username=username,\n                login_error=login_error,\n                custom_html=self.authenticator.custom_html,\n                login_url=self.settings['login_url'],\n                authenticator_login_url=self.authenticator.login_url(self.hub.server.base_url),\n        )\n\n    def get(self):\n        self.statsd.incr('login.request')\n        next_url = self.get_argument('next', '')\n        if (next_url + '/').startswith('%s://%s/' % (self.request.protocol, self.request.host)):\n            # treat absolute URLs for our host as absolute paths:\n            next_url = urlparse(next_url).path\n        elif not next_url.startswith('/'):\n            # disallow non-absolute next URLs (e.g. full URLs to other hosts)\n            next_url = ''\n        user = self.get_current_user()\n        if user:\n            if not next_url:\n                if user.running:\n                    next_url = user.url\n                else:\n                    next_url = self.hub.server.base_url\n            # set new login cookie\n            # because single-user cookie may have been cleared or incorrect\n            self.set_login_cookie(self.get_current_user())\n            self.redirect(next_url, permanent=False)\n        else:\n            if self.authenticator.auto_login:\n                auto_login_url = self.authenticator.login_url(self.hub.server.base_url)\n                if auto_login_url == self.settings['login_url']:\n                    self.authenticator.auto_login = False\n                    self.log.warning(\"Authenticator.auto_login cannot be used without a custom login_url\")\n                else:\n                    if next_url:\n                        auto_login_url = url_concat(auto_login_url, {'next': next_url})\n                    self.redirect(auto_login_url)\n                    return\n            username = self.get_argument('username', default='')\n            self.finish(self._render(username=username))\n\n    @gen.coroutine\n    def post(self):\n        # parse the arguments dict\n        data = {}\n        for arg in self.request.arguments:\n            data[arg] = self.get_argument(arg)\n\n        auth_timer = self.statsd.timer('login.authenticate').start()\n        username = yield self.authenticate(data)\n        auth_timer.stop(send=False)\n\n        if username:\n            self.statsd.incr('login.success')\n            self.statsd.timing('login.authenticate.success', auth_timer.ms)\n            user = self.user_from_username(username)\n            already_running = False\n            if user.spawner:\n                status = yield user.spawner.poll()\n                already_running = (status == None)\n            if not already_running and not user.spawner.options_form:\n                yield self.spawn_single_user(user)\n            self.set_login_cookie(user)\n            next_url = self.get_argument('next', default='')\n            if not next_url.startswith('/'):\n                next_url = ''\n            next_url = next_url or self.hub.server.base_url\n            self.redirect(next_url)\n            self.log.info(\"User logged in: %s\", username)\n        else:\n            self.statsd.incr('login.failure')\n            self.statsd.timing('login.authenticate.failure', auth_timer.ms)\n            self.log.debug(\"Failed login for %s\", data.get('username', 'unknown user'))\n            html = self._render(\n                login_error='Invalid username or password',\n                username=username,\n            )\n            self.finish(html)\n\n\n# /login renders the login page or the \"Login with...\" link,\n# so it should always be registered.\n# /logout clears cookies.\ndefault_handlers = [\n    (r\"/login\", LoginHandler),\n    (r\"/logout\", LogoutHandler),\n]\n", "path": "jupyterhub/handlers/login.py"}], "after_files": [{"content": "\"\"\"HTTP Handlers for the hub server\"\"\"\n\n# Copyright (c) Jupyter Development Team.\n# Distributed under the terms of the Modified BSD License.\n\nfrom urllib.parse import urlparse\n\nfrom tornado.escape import url_escape\nfrom tornado import gen\nfrom tornado.httputil import url_concat\n\nfrom .base import BaseHandler\n\n\nclass LogoutHandler(BaseHandler):\n    \"\"\"Log a user out by clearing their login cookie.\"\"\"\n    def get(self):\n        user = self.get_current_user()\n        if user:\n            self.log.info(\"User logged out: %s\", user.name)\n            self.clear_login_cookie()\n            self.statsd.incr('logout')\n        if self.authenticator.auto_login:\n            self.render('logout.html')\n        else:\n            self.redirect(self.settings['login_url'], permanent=False)\n\n\nclass LoginHandler(BaseHandler):\n    \"\"\"Render the login page.\"\"\"\n\n    def _render(self, login_error=None, username=None):\n        return self.render_template('login.html',\n                next=url_escape(self.get_argument('next', default='')),\n                username=username,\n                login_error=login_error,\n                custom_html=self.authenticator.custom_html,\n                login_url=self.settings['login_url'],\n                authenticator_login_url=self.authenticator.login_url(self.hub.server.base_url),\n        )\n\n    def get(self):\n        self.statsd.incr('login.request')\n        next_url = self.get_argument('next', '')\n        if (next_url + '/').startswith('%s://%s/' % (self.request.protocol, self.request.host)):\n            # treat absolute URLs for our host as absolute paths:\n            next_url = urlparse(next_url).path\n        elif not next_url.startswith('/'):\n            # disallow non-absolute next URLs (e.g. full URLs to other hosts)\n            next_url = ''\n        user = self.get_current_user()\n        if user:\n            if not next_url:\n                if user.running:\n                    next_url = user.url\n                else:\n                    next_url = self.hub.server.base_url\n            # set new login cookie\n            # because single-user cookie may have been cleared or incorrect\n            self.set_login_cookie(self.get_current_user())\n            self.redirect(next_url, permanent=False)\n        else:\n            if self.authenticator.auto_login:\n                auto_login_url = self.authenticator.login_url(self.hub.server.base_url)\n                if auto_login_url == self.settings['login_url']:\n                    self.authenticator.auto_login = False\n                    self.log.warning(\"Authenticator.auto_login cannot be used without a custom login_url\")\n                else:\n                    if next_url:\n                        auto_login_url = url_concat(auto_login_url, {'next': next_url})\n                    self.redirect(auto_login_url)\n                    return\n            username = self.get_argument('username', default='')\n            self.finish(self._render(username=username))\n\n    @gen.coroutine\n    def post(self):\n        # parse the arguments dict\n        data = {}\n        for arg in self.request.arguments:\n            data[arg] = self.get_argument(arg, strip=False)\n\n        auth_timer = self.statsd.timer('login.authenticate').start()\n        username = yield self.authenticate(data)\n        auth_timer.stop(send=False)\n\n        if username:\n            self.statsd.incr('login.success')\n            self.statsd.timing('login.authenticate.success', auth_timer.ms)\n            user = self.user_from_username(username)\n            already_running = False\n            if user.spawner:\n                status = yield user.spawner.poll()\n                already_running = (status == None)\n            if not already_running and not user.spawner.options_form:\n                yield self.spawn_single_user(user)\n            self.set_login_cookie(user)\n            next_url = self.get_argument('next', default='')\n            if not next_url.startswith('/'):\n                next_url = ''\n            next_url = next_url or self.hub.server.base_url\n            self.redirect(next_url)\n            self.log.info(\"User logged in: %s\", username)\n        else:\n            self.statsd.incr('login.failure')\n            self.statsd.timing('login.authenticate.failure', auth_timer.ms)\n            self.log.debug(\"Failed login for %s\", data.get('username', 'unknown user'))\n            html = self._render(\n                login_error='Invalid username or password',\n                username=username,\n            )\n            self.finish(html)\n\n\n# /login renders the login page or the \"Login with...\" link,\n# so it should always be registered.\n# /logout clears cookies.\ndefault_handlers = [\n    (r\"/login\", LoginHandler),\n    (r\"/logout\", LogoutHandler),\n]\n", "path": "jupyterhub/handlers/login.py"}]}