def METHOD_NAME(self, request):
    """Ensure the request is valid.
    The protected resource calls the introspection endpoint using
    an HTTP POST request with parameters sent as
    "application/x-www-form-urlencoded".
    token REQUIRED.  The string value of the token.
    token_type_hint OPTIONAL.
    A hint about the type of the token submitted for
    introspection.  The protected resource MAY pass this parameter to
    help the authorization server optimize the token lookup.  If the
    server is unable to locate the token using the given hint, it MUST
    extend its search across all of its supported token types.  An
    authorization server MAY ignore this parameter, particularly if it
    is able to detect the token type automatically.
        *  access_token: An Access Token as defined in [`RFC6749`],
            `section 1.4`_
        *  refresh_token: A Refresh Token as defined in [`RFC6749`],
            `section 1.5`_
    The introspection endpoint MAY accept other OPTIONAL
    parameters to provide further context to the query.  For
    instance, an authorization server may desire to know the IP
    address of the client accessing the protected resource to
    determine if the correct client is likely to be presenting the
    token.  The definition of this or any other parameters are
    outside the scope of this specification, to be defined by
    service documentation or extensions to this specification.
    .. _`section 1.4`: http://tools.ietf.org/html/rfc6749#section-1.4
    .. _`section 1.5`: http://tools.ietf.org/html/rfc6749#section-1.5
    .. _`RFC6749`: http://tools.ietf.org/html/rfc6749
    """
    self._raise_on_bad_method(request)
    self._raise_on_bad_post_request(request)
    self._raise_on_missing_token(request)
    self._raise_on_invalid_client(request)
    self._raise_on_unsupported_token(request)