'Ensure the Bearer token is valid and authorized access to scopes.
:param token: A string of random characters.
:param scopes: A list of scopes associated with the protected resource.
:param request: The HTTP Request (oauthlib.common.Request)
A key to OAuth 2 security and restricting impact of leaked tokens is
the short expiration time of tokens, *always ensure the token has not
expired!*.
Two different approaches to scope validation:
1) all(scopes). The token must be authorized access to all scopes
associated with the resource. For example, the
token has access to ``read-only`` and ``images``,
thus the client can view images but not upload new.
Allows for fine grained access control through
combining various scopes.
2) any(scopes). The token must be authorized access to one of the
scopes associated with the resource. For example,
token has access to ``read-only-images``.
Allows for fine grained, although arguably less
convenient, access control.
A powerful way to use scopes would mimic UNIX ACLs and see a scope
as a group with certain privileges. For a restful API these might
map to HTTP verbs instead of read, write and execute.
Note, the request.user attribute can be set to the resource owner
associated with this token. Similarly the request.client and
request.scopes attribute can be set to associated client object
and authorized scopes. If you then use a decorator such as the
one provided for django these attributes will be made available
in all protected views as keyword arguments.
:param token: Unicode Bearer token
:param scopes: List of scopes (defined by you)
:param request: The HTTP Request (oauthlib.common.Request)
:rtype: True or False
Method is indirectly used by all core Bearer token issuing grant types:
- Authorization Code Grant
- Implicit Grant
- Resource Owner Password Credentials Grant
- Client Credentials Grant'

def validate_bearer_token(self, token, scopes, request):

    raise NotImplementedError(u'Subclasses    must    implement    this    method.')
