code: def verify_plaintext(request, client_secret=None, resource_owner_secret=None):
      
      signature = sign_plaintext(client_secret, resource_owner_secret)
      match = safe_string_equals(signature, request.signature)
      if not match:
          log.debug('Verify PLAINTEXT failed')
      return match
docs: Verify a PLAINTEXT signature.
  
      Per `section 3.4`_ of the spec.
  
      .. _`section 3.4`: https://tools.ietf.org/html/rfc5849#section-3.4