code: def extract_bearer_token_from_http_request(parsed_request=None, authz_header=None):
      # type (Optional[Mapping[str, str]], Optional[str] -> str
      
      if authz_header:
          # Authorization Request Header Field: https://tools.ietf.org/html/rfc6750#section-2.1
          if authz_header.startswith(AccessToken.BEARER_TOKEN_TYPE):
              access_token = authz_header[len(AccessToken.BEARER_TOKEN_TYPE) + 1:]
              logger.debug('found access token %s in authz header', access_token)
              return access_token
      elif parsed_request:
          if 'access_token' in parsed_request:
              """
              Form-Encoded Body Parameter: https://tools.ietf.org/html/rfc6750#section-2.2, and
              URI Query Parameter: https://tools.ietf.org/html/rfc6750#section-2.3
              """
              access_token = parsed_request['access_token']
              logger.debug('found access token %s in request', access_token)
              return access_token
  
      raise BearerTokenError('Bearer Token could not be found in the request')
docs: Extracts a Bearer token from an http request
      :param parsed_request: parsed request (URL query part of request body)
      :param authz_header: HTTP Authorization header
      :return: Bearer access token, if found
      :raise BearerTokenError: if no Bearer token could be extracted from the request