docs: def signature(cert, sig, body):
      """Validate data request signature.
  
      See `validate.request` for additional info.
  
      Args:
          cert: cryptography.hazmat.backends.openssl.x509._Certificate. The Amazon
              signing certificate.
          sig: str. Signature header value sent by request.
          body: str. HTTPS request body.
  
      Returns:
          bool: True if valid, False otherwise.
      """
      body = six.b(body)
  
      sig = base64.decodestring(sig)
      padder = padding.PKCS1v15()
      public_key = cert.public_key()
      try:
          public_key.verify(sig, body, padder, hashes.SHA1())
          return True
      except InvalidSignature:
          warnings.warn('Signature verification failed.')
          return False