class_docstr: Abstract implementation of OpenID and Attribute Exchange.
  
  Class attributes:
  
  * ``_OPENID_ENDPOINT``: the identity provider's URI.
class_docstr_tok: ["Abstract","implementation","of","OpenID","and","Attribute","Exchange",".","Class","attributes",":","*","``","_OPENID_ENDPOINT","``",":","the","identity","provider","'s","URI","."]
docstr: Returns the `.AsyncHTTPClient` instance to be used for auth requests.
  
  May be overridden by subclasses to use an HTTP client other than
  the default.
docstr_tok: ["Returns","the","`",".AsyncHTTPClient","`","instance","to","be","used","for","auth","requests",".","May","be","overridden","by","subclasses","to","use","an","HTTP","client","other","than","the","default","."]
code: def get_auth_http_client(self):
      """Returns the `.AsyncHTTPClient` instance to be used for auth requests.
  
      May be overridden by subclasses to use an HTTP client other than
      the default.
      """
      return httpclient.AsyncHTTPClient()
  
imports: from __future__ import absolute_import, division, print_function
  import base64
  import binascii
  import functools
  import hashlib
  import hmac
  import time
  import uuid
  from tornado.concurrent import TracebackFuture, return_future, chain_future
  from tornado import gen
  from tornado import httpclient
  from tornado import escape
  from tornado.httputil import url_concat
  from tornado.log import gen_log
  from tornado.stack_context import ExceptionStackContext
  from tornado.util import unicode_type, ArgReplacer, PY3
label_desc: Use image node_id 5 for calling the OpenIdMixin obj's underlying member method code with example usage: obj.get_auth_http_client() and returns: httpclient